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FAQs on Freshwater Diatom Algae & Their Control

Related Articles: Freshwater Algae & Control, Algae Eaters, Otocinclus, Loricariids, Siamese Algae Eaters/Crossocheilus,

Related FAQs: Freshwater Algae 1, Freshwater Algae Identification, FW Blue-Green Algae, FW Algicides, Algae Eaters, Aquarium Maintenance, Freshwater Aquarium Water Quality, Treating Tap Water for Aquarium Use, pH, Alkalinity, Acidity, Freshwater Algae Control, Algae Control, Foods, Feeding, Aquatic Nutrition, Disease,

brown algae control, FW 3/12/10
Hi crew!
I posted this question before about getting rid of my brown algae infestation and you instructed me to get some Amazon Frogbit of Indian Fern.
Well, it took me a while, but I finally found someone with some Frogbit.
It's been in the tank (240 gallon) about a week and doesn't seem to be having any affect yet.
<It doesn't magically stop the algae. But once it starts multiplying under good, strong light it [a] shades the tank, starving the algae of light; and [b] outcompetes the algae somehow, absorbing nitrate and phosphate before the algae can get and use these. That's the theory, anyway. Bottom line, in tanks with lots of fast-growing floating plants, you rarely see much in terms of algae.>
I was talking to a friend of mine the other day who told me that there was a salt water snail that can live in freshwater that eats the heck out of brown algae.
<Not quite. There are true freshwater Nerite snails that produce larvae that are planktonic and in some cases only develop in brackish or saltwater conditions. Presumably the larvae spread along the coastline and out to oceanic islands, thereby allowing the species to colonise streams and rivers where completely freshwater snails cannot go. Do see here:
And because the snail is saltwater by nature, it doesn't reproduce while in the freshwater.
<Correct. They do lay their eggs -- all over the place! -- but the eggs never become actual snails.>
Have you ever heard of a snail fitting this description?
Thank you!
<As ever with snails (and algae-eaters generally) don't fall into the trap of thinking by *adding* something to the tank you'll somehow fix an algae problem. By definition, adding more livestock always increases the rate of nitrate/phosphate accumulation, and in theory at least, more nutrients in the water means the algae can grow even faster. By all means include some Nerites within your all-around balance of plants, fish and water quality, but don't expect any algae-eater to be a "magic bullet" if the problem is already out of control. On the other hand, if the tank is basically algae-free, and all you're concerned about is the diatoms on the front glass, and you're cleaning these off only once a month or so, then Nerites will certainly work well, at about 1 specimen per 5-10 US gallons. Cheers, Neale.>

Brown Algae - 2/7/10
Good morning crew,
I've got a bit of a dilemma I hope you can help me with.
My 240 gallon freshwater aquarium has been up and running for about 5 1/2 months now. About 1 1/2 month ago brown algae began to appear. After about 2 weeks it was pretty bad. My LFS told me that it was just a sign of the last stages of the tank seasoning and that it would go away on its own soon.
Well, it's been over a month now and, while it seems to take a little longer for it to grow back on the glass after my weekly cleanings, it has not gone away yet. Also, I have some nice looking fake plastic boulders in the tank that
are covered with the stuff that are going to be a challenge if I am going to have to scrub them clean. I do weekly water changes of 50 to 75 percent (It's difficult to tell exactly because I allow my filtered water to trickle into my tanks sump for 8 to 16 hours. The sump has an overflow.)
<Without plants, algae is inevitable. Adding a clump of Indian Fern and some Amazon Frogbit will do the trick if you don't want to put live plants on the bottom of the tank.>
I've noticed a few "dots" of green algae on the glass while I'm cleaning.
<This is very tenacious stuff, and difficult to scrape away. A razor-edged algae scraper can work, otherwise you need to use an algae sponge most vigorously! Catch the stuff before it spreads. On the plus side, it tends to imply quite good water conditions and plenty of light, but its appearance tends to mean your existing algae-removal process isn't doing the job. Light scraping or wiping leaves it behind. Regular, proper cleaning prevents it from becoming established.>
Any ideas on how much longer it may take for this stuff to go away?
I don't want to put anything in the water that could possibly harm my livestock.
Thank you, Pat
<Cheers, Neale.>

Re: Brown Algae 2/9/10
Any ideas on where I might purchase these plants online. I'm not having any luck.
<I'm in the UK, so that's the only place I can speak about from experience.
I've received good plants from both Java Plants and Green Line.
You'd also want to visit the Tropica site, and have a look on their "Dealers" page to find a retailer near you. Even if that retailer doesn't have Indian Fern (Ceratopteris thalictroides) or Amazon Frogbit (Limnobium laevigatum) in stock, they will certainly be able to order them in for you.
Finally, do try getting in touch with your local aquarium club. This is BY FAR the best value way to obtain aquarium plants. By their nature, aquarium plants are "weeds", and once established, most folks end up with cuttings they're only to happy to share with others.
Cheers, Neale>
Re: Brown Algae 2/9/10
Do you know if Amazon Frogbit is also known as Java Fern?
<No, it isn't. Java Fern (Microsorium pteropus) is a slow growing epiphyte, not a floating plant. Java fern is completely useless for algae control. It grows very slowly, and in fact is more likely to become an "algae magnet",
getting covered with hair algae and the like. The same holds true for Anubias, another epiphyte commonly traded. Both great plants, but useless
for algae control. Cheers, Neale.>

algae eater question 05/21/09
I have a 40 gallon long aquarium that is stocked with 2 Gourami, 5 julii Corys, 3 brilliant rasbora. I am finally starting to see algae on my glass (brownish spotting).
I was wondering if I should get a Pleco or how quick it will out grow the tank.
<"No" and "very quickly".>
My other thought was some Oto's and if I go that route how many is recommended for a 40 gallon.
<Otocinclus don't eat diatoms, they eat green algae. The best solution to diatoms is the introduction of lots of fast-growing plants and strong lighting. This works amazingly well. Adding one or two Nerite snails per 10 gallons can help too, but in my experience, only alongside the fast-growing plants, not instead. If plants don't appeal, then a suitable algae scraper is the other alternative.>
Thank you
<Cheers, Neale.>

What is Brown stuff growing on tank glass? -- 04/12/09
I've written you before and you've been way helpful.
<Thanks Frank. And please, help us by sending images no bigger than 500 KB in size; we have only 10 MB of file space for e-mail, and your message used up a good couple of MB right from the start, filling our account, and bouncing back other peoples' messages.>
Here's another question. What is the brown stuff growing on my tank glass?
It also grows on my fake plants and ceramic aquarium decorations. I thought it was the helpful bacteria that eat the Nitrites. But now I believe that my helpful bacteria is white/grayish and it grows on everything. This brown stuff isn't so attractive and if it's not a particularly helpful organic then I'm eager to scrub if off my tank walls.
See attached photos with brown "smears" on back of tank wall beneath filter. You can also see the mystery brown organic on the green/white artificial plant leaves and on the large white stones. Below are my tank
50 Gallon freshwater tropical
2 Aqua Clear 70 Filters, elements in filters changed on an 8-12 week schedule
Tank is 5 months old
30-40% Partial water change weekly until 4 weeks ago, now partial change every two weeks.
Fish are fed flakes & micro pellets several times daily every 2-3 days
Tank is in room with tons of natural light. Tank has two 15 watt bulbs that are on infrequently
6=Buenos Aires Tetras
1=Pearl Gourami
1=Albino Cory Cat
3=Emperor Tetras
3=Pink Tetras
7=Neon Tetras
2=Praecox Rainbows
2=Red Wagtail Platy
2=Sunset Wagtail Platy
<Just common or garden diatoms. Nothing serious. Very common in poorly lit tanks, and direct sunlight certainly encourages diatom growth on the glass where the light hits the glass. No real cure beyond increasing the light level to 2 watts per gallon and adding lots of fast-growing plants. Cheers, Neale.>

Re: What is Brown stuff growing on tank glass? -- 04/12/09
Neale, I'm so sorry for the large pictures, I didn't know they caused that kind of trouble.
<Unfortunately yes, our e-mail account isn't all that big; while fine for text mails, if we get too many photographs that aren't resized downwards, we have problems. On the page where our e-mail address resides, it does say something about this, and our request for relatively small images.>
And thank you for the reassurance about the brown stuff.br /> <Happy to help.>
Actually, last week I started the process of changing out all my artificial plants with live ones and I ordered a high wattage lamp fixture.
<That should help dramatically. I have messy tanks with messy fish, and yet wipe down algae maybe once ever couple of months. How come? I use lots and lots of fast-growing plants. Vallisneria, Hygrophila, Limnobium laevigatum, Indian Fern... all work well. A few Nerite snails will also help, and because they don't breed in aquaria, population explosions aren't an issue.
Allow one or two per 10 gallons.>/> Thanks for the excellent specific advice. Take care.
&<Good luck, Neale.>

Brown Algae, FW 8/16/07 Hello. <Ave.> I have had a 20 gallon freshwater tank for over a year now. I have four black skirt tetras, three red spot phantom tetras, two small catfish, 1 neon, 1 Mickey mouse platy, and one called a tequila sunrise. (I not sure of the proper names for all these fish, some of them my girls pick because they like the store names! The singles are left over from larger groups that have dwindled.) <Ok.> Recently I've been getting brown algae in the tank. I went to the local pet store and purchased an golden algae eater and after reading your website I believe it's the one you don't recommend, the CAE. It's seems to be fine now, about 3 inches long, and IS working on the algae. I don't know if the pet store will take it back. What to do? <Do what I do. Ignore everything but the algae on the front glass. Algae doesn't harm the fish. Algae doesn't damage anything. Algae looks more natural than clean sand and rocks. The fish like to eat algae. In other words, there's nothing wrong with it. Brown algae is diatoms. No fish eats this in significant amounts. All the "algae eating" fish in the trade prefer a different group, the Chlorophyta or green algae. So adding algae eating fish is usually a complete waste of time. Furthermore, adding fish to a tank means there's more nitrate/phosphate in the water, and this allows the algae to grow faster. In other words, adding an algae eater can make things worse!> What measures do you recommend for algae? <Only two things work. First, old fashioned elbow grease. Get an algae sponge. Scrape off algae you don't like. Siphon away. Repeat every week or as often as required. Second, use plants. Fast growing plants (not Java ferns!) somehow -- for reasons not fully understood -- stop algae from growing. Fast-growing clumps of Vallisneria, hornwort, Cabomba, Elodea, etc do this amazingly well. If your plants are growing so fast you are cropping them back every week or two, you will have almost no algae. It sounds like magic, but it's true. Plants have to do this in the wild, or they'd be smothered with algae. But yet, wild aquatic plants are largely algae-free except where the leaves are old or damaged. It's the *rapid growth* that seems to be the key. Anyway, while this sounds contradictory, an aquarium with LOTS of light and a well-fertilized substrate and enough CO2 will have plants growing happily and yet almost no algae. There may be some green algae, but here is where your algae eaters come in. Add a few algae eating fish/snails/shrimps and lo and behold, problem fixed.> I just reduced my lighting timer from 13 hrs. to 10 hrs. What is the recommend lighting duration? <Tropical plants want 12 hours. Some people break this into 6 hours on, 2 hours darkness, and 6 more hours on. This "siesta" seems to harm algae but not plants. Seemingly, plants (which are physiologically much more advanced) adjust readily, but algae cannot, and so grow less rapidly. Now, that's the theory. If you have a major algae problem, I can guarantee it won't work. But if you have fast-growing plants and the algae is basically declining, this siesta trick does seem to be the icing on the cake.> I tried planting live plants (started with plastic) but haven't had much luck! I know they're good for the tank and the fish. What plants do you recommend for a tank my size? <People who have "no luck" with plants almost always fail to provide sufficient light. To thrive, the sorts of fast growers I'm mentioning need 2 watts of light per gallon, preferably with reflectors behind the lights as well. Anything less just won't work. Now, the problem is a lot of "all in one" aquaria have piddling little lights that put out 1 to 1.5 watts per gallon. This is fine for the fish, and you might get Java fern and Anubias to do well, but those plants grow too slowly for algae to be affected. Furthermore, Diatoms seem to thrive under dim light better than any other algae, and that's your problem. So, you need to (likely) double the lighting. The more the better, really. Add a nutrient-rich substrate (laterite mixed with gravel and then topped with plain gravel works well). Plant some fast growing plants. Sit back, and enjoy your algae free aquarium.> I appreciate your help! Jon <Hope this helps, Neale.>

Mysterious Catfish Deaths (and brown algae) -- 07/03/07 Hi crew, <Hello.> This is my first time writing to you. I have been an avid reader of your pages for almost a year, and I have gathered much information. I have also kept fish for quite a long time, and I have never encountered these problems. <OK.> Firstly, aquarium stats: 29 G glass bowfront, about 6 months old. Inhabitants include 3 green cories, 3 Oto, 1 medium angelfish, 4 various platies, 2 neon rainbowfish. Moderately planted (a couple of swords, sparse java moss, a couple java ferns, some floating elodea), 24 W T-5 lighting, no CO2 or air pump, filter for 60 G (300GPH). Ammonium, Nitrites = 0, Nitrates = 10 ppm. Substrate = Eco Complete. 1 piece of driftwood. pH = 8.x? (it is really high, and the tests have not been very accurate). Water changes are 25 - 30% once a week (very regular), siphoning the unplanted areas and under the driftwood and replacing with treated tap. <The high pH is alarming. It may be an issue with your test kit. Test kits designed for the "low end" around pH 5.5-7.5 tend to be inaccurate at the "high end" around pH 7.5-9.0, and vice versa. So, check that. Second, what's the pH of the water straight out the tap? Your selection of fish wants a pH around 7.2-7.5, but what matters more than pH is hardness, so you want to check that as well. If you live in an area supplied with exceptionally hard water (such as water from a limestone aquifer) you can easily have a pH slightly above 8.0. Not ideal for things like tetras and angels, though they can adapt.> Issues: Cories with degenerating barbels/fins. The cories (had 6 at first) were fine for the first few months. They grew from baby size into adult size and were super active. They also had nice fins and barbels. Then, java moss began growing everywhere, and their barbels started deteriorating. Then a couple died. I thought it might be the Java Moss collecting debris and making high local nitrates. But I cleared out almost all of it and the cories still seem to be suffering from fin rot/barbel degeneration. I put in a new Cory from QT a few weeks ago and it's barbels seemed to be deteriorating! Then it died. Why is this? All the mid to top dwelling fish (including the angel) are active and eating very well, and have nice fins. Also, the cories seem lethargic and hide under the driftwood all day, only coming out to get food. <Almost certainly the water quality at the bottom of the tank and especially in the substrate is suboptimal. The reason the new Corydoras died was it couldn't adapt to these conditions, whereas the old Corydoras have (to a degree) adapted. Anyway, check the water circulation. Many filters do a good job of moving water around the top of the aquarium but the water flow at the bottom can be relatively poor. If the Java Moss is accumulating silt, then that's a good clue that this might be the problem. Adjust the filter, or add an airstone or two at the bottom of the tank to improve water circulation.> Additionally, the otos like to hang out near the top of the tank. If I recall, they used to like hanging out on the plants. But there seems to be something bothering them because they hang near the surface and don't eat much algae. This lead me to think there was something near the bottom that bothers them, but I can't identify it. I do siphon the unplanted areas of the bottom every time I do a water change. <Sounds as if there's a lack of oxygen at the lower levels, again suggesting poor water flow. Otocinclus are fishes of fast-flowing streams, and are exceptionally sensitive to static water.> Is the Eco Complete doing something strange to the fish? What could the culprit be? Usually fin rot is associated with nitrates but I tested the water at the bottom of the aquarium, and the nitrates were at 10 ppm! (same as the surface). <I can't imagine the Eco Complete is the immediate problem. Are you using under tank heating of any kind? When using deep, rich substrates, under tank heating is recommended. Basically you thread a heater cable through the substrate, and when this is warm, it sets up convection currents that slowly circulates the water. Works very well and the plants thrive, but it's a little more expensive to do than a regular heater.> Finally, a there is a large amount of brown algae infestation in my tank. It is covering all of my plants and the java moss too, making it a furry brown carpet. To the best of my knowledge, it doesn't seem like there should be a lot of algae. Is the lighting causing this? I don't have a CO2 system, and it is not convenient for me to install one, so I was wondering if there was any other way to combat this problem. I don't mind the algae on the glass, because I can scrape it off, but the algae on the plants is what's bothering me. <Brown algae -- diatoms -- are almost always a problem in [a] new aquaria and [b] tanks with insufficient light. If your tank is more than a few months old, then the problem is probably lack of light. Fish and snails have modest impact on brown algae though they do eat some. Much better to boost the lighting levels. For various reasons plants prevent algae from growing when they are doing well. So make sure you have at least 2 Watts per gallon of water, and that you are using the right type of light (i.e., a plant-friendly one rather than a generic aquarium light).> Thanks for your advice, Alex <Good luck, Neale>

Diatom bloom in a new tank with no ammonia, nitrites or nitrates 5/25/07 Hello, WWM Crew! Thanks for your site; I've found lots of good information. <Hello and thanks!> I hope you can help. I will be detailed in the description of my problem, figuring too much information is probably better than not enough information. I've had a rocky start setting up my first ever freshwater tank (55 gallon glass tank, Penguin 350 filter with four Ready-To-Use charcoal-containing cartridges, fluorescent lights, decorated with well-rinsed white gravel, obsidian rock, black river stones, driftwood and plastic plants). My cycle has not proceeded in a typical textbook fashion; in fact, the staff at the LFS considers my tank to be a bit of an anomaly, I'm afraid. It's been up and running for 49 days. <All the hardware sounds fine. Personally, I'd bin the carbon, but otherwise make 100% sure you remove the carbon any time you medicate the tank. Lots of people forget, and the carbon removes the medicine, and the fish die. A 49-day cycle to mature the filter sounds a lot though. Not impossible though. But certainly within 60 days most tanks are fully cycled. Depends somewhat on temperature and water chemistry.> I started a fishy cycle on April 7 with three gold dust mollies (1 male, two females) and 3 Mickey mouse platies (1 male, two females). Seven cardinal tetras and two male "honey sunset" gouramis were added 15 days later; three tiny baby kuhli loaches and 3 rainbowfish (one female, not sure about the sex of the others) were added last weekend. <My issue here is the selection of fish. I feel I am saying this two or three times a week, but mollies and tetras cannot be mixed. Mollies need hard, alkaline water to do well. Ideally, they need brackish water conditions. Neons and cardinals like soft and acidic water. Ergo, keep them together and one or other will be in suboptimal conditions. There's no "happy medium".> Seeding material (muck squeezed out from a filter) was provided by the LFS; Biospira was added on day 41. <Filter squeezing aren't really very helpful. The bacteria are in the sponges (or whatever) not the water. Filter sqeezings is basically just dirty water. Some bacteria perhaps, but not much, certainly not enough to make a big difference to the cycling of an aquarium. Biospira, as I understand it (never used it) should be added at Day 1 along with some fish, because the Biospira colonises the filter immediately.> I'm feeding small amounts of flake food twice daily which the fish scarf down in 30 seconds or less. <Good. Don't forget mollies are vegetarians, and need green foods more than flake. Or at least, *vegetarian* flake food. Not regular flake food. Sushi Nori is also popular with them.> I filled the tank with tap water that had an unusually low pH for this area (LFS says our water authority adds stuff that alters the pH during periods of heavy rains, which we've had this spring). pH was around 6.8-7.0 at start up; it's gone up, slowly, over the past six weeks and is now around 7.2. <Way WAY too low for mollies. Mollies need "hard" to "very hard" on whatever test kit you are using, and a pH of 7.5 to 8.0. Nitrates, by the way, must be less than 20 mg/l for mollies to have even a reasonable chance of staying healthy in freshwater aquaria. In brackish water they are orders of magnitude more robust, which is why I would insist that people keep them thus, if I could.> The pH of the tap water has also gone back up to its typical 8.4; the increase in the tank pH is probably due to water changes with higher pH water, but it could be something else. GH of both tap and tank water are a steady 120 ppm and KH is at 40 ppm (moderate hardness and low total alkalinity are typical for our tap water). <Sounds pretty uninspiring to me. A high pH and high alkalinity is good for hard water fish like livebearers. But a high pH and low alkalinity is pretty rubbish, and not favoured by anything much. If this was me, I'd return the cardinals and the gouramis, and create a hard water aquarium with a calcareous substrate (e.g. coral sand) and keep fish suited to high pH and hardness: livebearers, rainbowfish, gobies, some killifish, some cichlids, and so on. But that's me.> Whenever the tank KH drops to zero, a 15% water change brings it back up to 40. <OK, this is something that you want to avoid. Fish will adapt to slow changes in water chemistry, even where the changes are to the worse. But swinging the water conditions up and down will do them harm in the long run.> The water is conditioned with "Prime" and I'm careful to match temps during water changes. Tank temperature remains steady at 78-79 degrees (digital thermometer) with a Stealth Visi-Therm heater. <Temperature changes aren't really that critical. Freshwater fish get exposed to significant temperatures all the time. But what you're doing is sensible.> I started out testing with Mardel 5-in-1 test strips, then switched to API freshwater liquid reagent test kits; I've also taken a sample of tank water to the LFS each week for testing, and I have a Seachem "Ammonia Alert" hanging in the tank. None of the test kits/strips are expired and I'm careful to shake the bottles of the reagents well and to mix the nitrate sample well as directed. I've gotten similar results from all these various testing methods, however, the test strips aren't as precise (they don't measure nitrate between 0 and 20, whereas the API test kit measures nitrates of 5 and 10). <There's margins of error in any test kit. In this instance, it's apparent the nitrates are quite low. Precisely what they are doesn't matter that much. Anything between 0 and 20 mg/l nitrate is fine.> I got cloudy water as expected on the third day after setup which cleared by day 6. By day 6, however, a significant amount of particulate matter appeared in the clearing water that hasn't completely abated and doesn't respond to water changes. <Possibly silt from the sand/gravel. I find changing the filter floss makes a big difference here. Some water cloudiness is common in new aquaria. Provided the ammonia and nitrites are tending towards zero (or better yet, at zero) don't worry about it.> I expected the ammonia to rise next, but I had no appreciable ammonia until day 30. <Odd.> Nitrites actually appeared first, on day 21, at 0.5; I did a 15% water change (first water change) and they dropped to zero. I continued to do 15% water changes every 2-3 days as the nitrites would rise back up to 0.5. This was against the advice of the LFS, who recommended no water changes until the cycle was complete, but I'd read elsewhere that the nitrifying bacteria live on the filter media and the surfaces of the decorations, not in the water, plus I'd lost a fish and one fish had some fin problems (see below) so I felt the water changes were necessary. I also rinsed out the filter cartridges in the old tank water and vacuumed about a quarter of the gravel with each water change (white gravel was probably not the best choice, in hindsight; it's like white carpet). <You are correct to do water changes. The LFS advice was questionable here. All the "action" happens in the filter, not the water, so even changing 50% of the water daily wouldn't do any harm. I agree with you about the white gravel. Apart from looking terrible, it also makes the aquarium very bright, and the fish hate light being reflected from underneath (doesn't happen in the wild) and consequently tend to subdue their colours. Cardinal tetras, for example, only look their best in dark tanks with black sand and tea-coloured water. Until you've seen them thus, you really haven't seen them at all.> On day 30, I got my first positive ammonia reading of 0.25. The nitrites had also risen to 1.0, so I did a substantial water change of 40-50%. The ammonia dropped back to zero and remains zero to this day. The nitrites dropped to 0.25 after the water change, then rose to 0.5 over a two day period and remained there until day 36, when they dropped to 0.25 then disappeared on day 40, with no water changes for those 10 days. (The LFS suggested I minimize my water changes during the cycling period, stating the nitrites "had" to spike to get through the cycle.) <All weird. It doesn't really matter much what the numbers are. This is biology, and the graph you see in aquarium books is schematic, not accurate. The reality is that there are changes in the bacteria flora in an aquarium all the time, but provided overall water quality stays good, that's all that matters. I personally would stick with a water change routine of 50% per week regardless of what the LFS says.> According to everything I've read, the nitrates should be rising now that the ammonia and nitrites are at zero. However, my nitrates are zero, always have been. The clerk at the LFS "thought" she saw a "tiny amount" of nitrates when she checked a sample last weekend and declared the tank "cycled", but I have gotten zero nitrate readings since day 1. <Nitrates typically rise quite steadily because they aren't "going anywhere" in the aquarium. So they accumulate over time, dropping down at water changes, and then going back up again.> Brown diatom "algae" began appearing on the filter intake, the glass and one of the plastic plants on day 36; I wiped it off, it slowly came back. Over the past two days, the brown algae has spread over the white gravel and onto the white portions of the obsidian rocks at a rather frightening rate. <Get over it. Algae is part of any aquarium. It's harmless. All algae means is the tank is "unbalanced", that is, there's no plant growth to compensate for the nutrients dumped in the water by the fish. In a planted tank, algae grow at a rate inversely proportional to the growth of plants. Your LFS will probably try to sell you an "algae eating" fish. Resist this, and instead install stronger lights (if you don't already have them) and add some fast-growing plants. Far more effective.> I decided to start weekly 15% water changes two days after adding the Biospira. I did a 15% water change with a light gravel vac a few days ago and although it hasn't been a full week, I will do another today... <Good.> ...(the diatom algae on the gravel looks awful). <Well, I didn't choose the stuff. Honestly, an aquarium has to look pleasing, otherwise they become a chore. Take out what you don't like, and replace with something nicer. In the long run, you know it makes sense. Even gravel from the garden centre works fine, so needn't pay the mark-up on gravel at the fish shop.> The current inhabitants of the tank are doing well. I did lose one of the gouramis a week after I got them; it had a big red sore on its side. The other gourami is thriving. <You have Dwarf Gourami Disease. Again, I seem to be saying this on a weekly basis as well. All, repeat all, mass produced dwarf gouramis are exposed to this bacterial/viral disease (or variety of diseases). Once they leave the fish farm, where they are tanked up on drugs, they weaken, become lethargic, lose their colour, develop sores, and die. Your other gourami has a better than 50% chance of being infected and will likely die within a few months. Sorry. My only advice is DON'T but dwarf gouramis. But other species, such as Colisa labiosus (thick-lip gourami) and Colisa fasciata (banded gourami) that look similar but are a little bigger and far more robust (immune to this disease, apparently). Dwarf gouramis are a classic example of how capitalism shouldn't work: because we want cheap fish in bright colours, we tolerate poor animal husbandry and casual use of antibiotics. End result: dead fish, wasted money.> One of the platies seems to be a bit of a runt; the gouramis nipped its caudal fin when they were introduced but it's grown back; now, the biggest molly is picking on it, and we noticed four days ago that part of his left pectoral fin is missing, but it appears to be growing back as well, with no treatment. "Stubby" eats well and zooms around the tank despite his fin issues. <Still, I'd treat for fungus and finrot nonetheless. There are medications that do both at once. Remove the carbon from the filter! Mollies can be very aggressive to platies, so in the long term increasing the number of platies might help diffuse the tension a bit.> One of the platies gave birth once (found dead fry on the filter) and another is pregnant. <Platies are lovely fish. If you converted to a proper hard water system and got rid of the cardinals, you could keep lots of other interesting livebearers alongside them. It's well worth getting to know the livebearer group in more depth. See here: http://www.wetwebmedia.com/FWSubWebIndex/livebearers.htm and here: http://www.wetwebmedia.com/FWSubWebIndex/poeciliids.htm > Sorry, I know that was long. If you've made it this far, perhaps you can answer these questions for me: <MORE!!!!> 1. Why do I have no nitrates after 49 days and with zero nitrites? Something in the tank is converting ammonia to nitrite and nitrite to, well, something, otherwise I would have positive ammonia and nitrite readings; but the ammonia and nitrites are both zero, as are the nitrates. <No idea why. Don't fuss. So long as ammonia and nitrite are zero, the rest is fine.> 2. Why do I have this obnoxious brown algae/diatom bloom with no nitrates in the tank for the past 49 days? The nitrates were zero before the diatoms showed up and they're still zero; what on earth are they feeding on? <Diatoms are common in new tanks, and tend to die back after a couple of months. Remove them from the front glass with a sponge but otherwise ignore them. They're part of nature and the fish like them. Actually amazingly beautiful under a microscope. Do a little Googling and see!> 3. What is this particulate matter (looks like dandruff or dust) in the tank? <Perhaps silt, perhaps bacteria. Either way, usually clears up. Change the filter floss.> 4. What should I do to get rid of the algae and the particulate matter? I don't really have room to add a bunch of otos. <As said, will go away themselves. Healthy, fast-growing plants will eliminate algae amazingly well.> 5. What else am I missing? What should I be doing that I'm not currently doing? <Quite possible missing an aquarium book. The value of sitting down, reading, learning cannot be overstated.> Thanks for your time and attention, Caroline <Cheers, Neale>

Re: Diatom bloom in a new tank with no ammonia, nitrites or nitrates -- 5/25/07 Thanks so much, Neale, for such a quick response and excellent advice. I will start feeding the mollies some veggies, take the filter carbon out and treat the platy for fungus and fin rot (any suggestions as to treatment?)... <Whatever is cheap and available in your area. All the common brands seem to work well.> ...bump the weekly water changes up to 50% (which should also help keep the KH from dropping to zero, right?)... <Correct.> ...look into replacing the gravel with a darker-colored coral sand and stop worrying about the algae and lack of nitrates. <Don't worry too much about what substrate you use. The buffering effect of substrate isn't huge. It helps, but it isn't a huge factor. So if you find something you like the look of -- say, black sand, which really improve the colours of the fish -- the use the sand but add some calcareous material to the filter intead. You can buy filter media bags (or use the "feet" from old nylon tights/pantyhose) and stuff them with crushed coral or crushed seashell. Pop them in the filter, and these will harden the water as it washes by. You need to clean them every couple of months because the bacteria coat them and isolate the calcium carbonate from the water, but that's a pretty easy job (hot water does the trick). Or you can simply put the media in the sunshine to let the UV burn away the bacteria, while using a second batch in the filter for the time being.> A brackish tank with plants sounds wonderful and I want my fish to be happy, but I haven't even gotten the hang of freshwater fishkeeping yet! <In some ways, brackish is *easier*. Fewer diseases for one thing: most of the common diseases in freshwater won't survive in brackish water, or are at least less frequently seen. The brackish water also buffers the pH and hardness "automatically" because the marine salt mix contains water hardening chemicals.> Just looking at the brackish FAQ on WWM was a bit intimidating; I can easily imagine myself messing up the salinity and killing off fish, plants, nitrifying bacteria or all three! <Not very likely. Brackish water organisms by definition have to be hardy and adaptable, because they live in an environment where the conditions change rapidly. Once set up, brackish water tanks are remarkably easy to care for. Really, the only extra step to learn is making up the water, but even that is quite easy if you take your time and try and understand what you're doing. The range of brackish water fishes is surprisingly broad, and new species such as gobies and livebearers and halfbeak are turning up in the hobby pretty much all the time. There are also the lovely Nerite snails, pretty little algae-eating things that don't breed in aquaria. Be sure and have a read of this: http://www.wetwebmedia.com/ca/volume_4/V4I2/Brackish%20Systems/brackish.htm > There's so much to learn and I don't have a good book (I seem to have a rather outdated book); much of what I've read has been on the Internet, and the quality of information on other sites seems so variable, much like listening to LFS staff. <Indeed. To be fair, there are differences in opinion about many things. I'm adamantly against the use of carbon and salt in freshwater aquaria, but others swear by the stuff. Some people have good luck keeping mollies in freshwater tanks, but most of the questions I get about mollies involve problems that could be avoided keeping them in brackish water. And so it goes on. Like any hobby, there are probably multiple ways to get the job done. But as a default position, trying to replicate conditions in the wild is always a good start. In this case, mollies and platies come from come from the hard waters of Central America whereas cardinals from the mineral poor black waters of the Amazon. Simply from that perspective, they're incompatible. If you're familiar with gardening at all, you'll recall that plants are choosy about things like soil type and light intensity. So it is with fish.> However, taking the cardinals and the gourami back to the LFS store is not an option; they'll only take back fish that die within 3 days of purchase, and only if the customer can furnish the original receipt and a sample of tank water (to prove tank conditions weren't the cause of their demise). The only other tank I have is a 2 1/2 gallon tank which I assume is too small for anything but a betta or a QT tank. <Agreed. Well, most of these fish should thrive at pH 7.0 to 7.5 at moderate hardness. The mollies are the ones I'd be unsure of, simply because something like 50% of the time mollies simply don't stay healthy in freshwater. Nitrate (or water quality generally) is probably the key, since mollies live in freshwater in the wild happily enough, it is only in aquaria they are plagued with fungus and finrot.> I have two friends with aquariums, but they're less conscientious about fishkeeping (and more overstocked) than I am. So I guess I need another tank. (I can't believe I'm going to need another tank. My husband already thinks I'm insane.) I'm guessing the 3 baby kuhli loaches would prefer living with the 7 cardinal tetras and the gourami than with the salt- and alkaline-loving livebearers; so what's the smallest size tank I could get that would suffice to house them all? <A 10-gallon tank for the tetras, loach, and gourami would be fine. I have one like this for cardinals, a few Corydoras, and a lone wrestling halfbeak that I had to "rescue" from another tank. It's filled with plants. The fish seem happy and healthy. In fact, my girlfriend thinks its the nicest tank I have because it is so overgrown with plants. It's one of those "all in one" systems with its own light, heater, and filter, so rather a nice thing to set up.> And to think I thought having an aquarium would be relaxing, ha ha. <We forget sometimes: fish are animals, not ornaments. To be sure, once stable (which takes a couple of months) fish tanks do become very low maintenance. Water changes once a week, food twice a day, and a filter clean every few months. But in return for patience and a little work, fish tanks give back a great deal.> Thanks again for the information, <No problems. Neale>

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