Freshwater Snails Overtaking My Tank   5/31/2010
Hello Everyone,
I have searched your site to try to find out the best way to rid my 20 gallon freshwater quarantine tank from snails.
<If it's a QT tank, then manual approach will work best. Strip the tank down, clean the tank, deep clean or replace the gravel, and that should be that.>
I received quite a few plants from someone and knew from past experiences that they would most likely have snails within the leaves.
<Can be the case; use a potassium permanganate dip. Take care not expose the plants for too long though, as snail-killing potions are harmful to plants.>
I set up a tank only for the plants so I can monitor them for a month or two to see if my suspicions were correct, and guess what, I was right. Now since there are no fish, I have been leaving the tank alone, with only co2 and some dechlorinator when I do a water change, roughly once a month hoping they would die from lack of food.
<The bigger problem is that the filter bacteria will die without a source of ammonia. So to a degree, the snails are helpful here, since they eat food and excrete ammonia.>
They don't seem to me eating my plants (I don't have any idea what types of plants or snails I have) but they eggs must have hatched recently. I have a good 50 babies latched onto glass, leaves, roots, etc. there is no gravel or decoration in the tank. Strictly plants.
<Dip the plants, siphon the remaining snails from the tank, and then return the plants.>
I just bought one of those cheesy snail catchers but I know that doesn't work very well and liquid snail killer is also a plant killer.
<Not if used for short periods, typically a 20-minute dip.>
I was squishing them but they are just too many snails with too many hiding spots. What should I do? If I continue to not feed, will they all just eventually die?
<Population size is certainly related to food availability, so eventually yes, population will drop to that supported by ambient algal/protozoan growth.>
Some of the leave seem to be dying off which is causing some debris at the bottom.
<Snail food.>
Should I give it a good cleaning to get it all out of the bottom so the snails have nothing to feed off of?
<If you want.>
Thank you for your time.
Lisa
<Snails aren't really a big deal, so I tend to ignore them. Clea helena is a good snail-eating snail, and breeds quite slowly, so adding a few of these will control most snail populations nicely. Otherwise in themselves snails do little harm, barring a few species that eat plants. Cheers, Neale.> 
Re: Freshwater Snails Overtaking My Tank  6/1/10
Thank you for your reply Neale. Most people don't mind snails but I am one of the few that will do everything I can to avoid them.
<I see. Well, you're probably wasting your time here.>
I don't like them climbing everywhere and they multiply too fast which makes aquarium maintenance more work that I need.
<On the contrary, snails can be very useful for keeping aquaria clean.
Melanoides sp snails, the ones often called MTS or Malayan Livebearing Snail are the equivalent of earthworms, burrowing through the substrate removing organic matter and aerating the substrate. Now, can you have too
many of them? Sure. But when that happens it's a result of chronic overfeeding and/or under-cleaning of the substrate. Think about it: these snails need food to grow and breed. No food, no baby snails. It's like finding cockroaches in the kitchen, and blaming them for making the kitchen messy. No, the cockroaches are there precisely because a messy kitchen has lots of food for them.>
I am glad you mentioned the potassium permanganate but I have been unable to find this within any US Fish supplier. I found that Jungle brand liquid Water Clear has potassium permanganate in it but have not been able to buy it since only the tablets are what seem to be common. There is nothing to tell me if the tablets have the same active ingredient. Can you please point me in the right direction?
<Potassium permanganate is fairly toxic, so should be used with care. When dipping new plants, immerse them in a dilute "rose wine" coloured solution for 5-10 minutes. Rinse off the plants before putting them in the aquarium.
There's no real way to kill snails in an aquarium without risking the lives of your fish and plants. So ultimately snail control comes down to [a] keeping them out; [b] minimising waste food so snail populations cannot grow rapidly; and [c] stocking some type of snail-eating animal.>
Thank
Lisa
<Cheers, Neale.>

Last Check before First Trip, FW snails 5/11/10
Neale,
<Greg,>
Please help bring a couple things together that I understand in general but am not sure on my specifics.
<Yep.>
As a recap, in addition to four species of fish, I added four zebra Nerite snails to help with algae control and found a "baby" hitchhiker. Well, now I've found two more. Still to small to get a good pic of but they are growing very fast and I hope to God there are no more. I'm still baffled as to how they got there since I hand placed the much larger zebras by hand so they were upside up in the tank. I'm not sure the environment can handle a total of seven at 36 gallons!
<They aren't Nerites, I'm sure. Much more like Physa or similar.>
They also don't look like zebras at least at this point. More like apple or at least more cochlear. They are hard workers mostly clinging to fake plants but they are on the move just like their larger mates.
<I have Physa in planted tanks and they don't do any harm that I can tell.>
I'm not talking about his because I am some proud parent pleased to have more wildlife. Just the opposite, I'm looking for balance and have had enough problems with getting ammonia under control.
<Indeed.>
Is it possible that having a large crew of snails working fast on a tank will create ammonia that wouldn't otherwise be there?
<Not really.>
In other words, scraping algae doesn't create ammonia
<Yes it does.>
but having a snail eat and poop it does.
<Protein becomes ammonia, whether fish food, rotting vegetation, or baby snails. Just because algae and plant material contains a lower percentage of protein than animal material, it doesn't mean it's protein-free. Put another way, snails consume plant material, and appropriate the nitrogen in the plant material into their own tissues. They don't make protein from nowhere.>
I still like this better than scraping and honest the snails are extremely fascinating to watch and ponder the Creators intentions.
<Quite.>
The main question is, I know already that fish can go a bit without eating and that has a benefit of reducing ammonia from being increased over a few days.
<Indeed.>
I will be leaving town this upcoming Saturday at around 4pm and returning the following Thursday around 2pm.
<They don't need feeding for this short period. If you feel the need, leave a slice or two of cucumber or a piece of lettuce, and they'll nibble on that.>
What is your recommendation for me specifically please? I want to do a water change and would like to know what percent you recommend for this scenario and what to do about feeding. I know three days is OK but five seems pushing it. Would a two day weekend feeder be a good idea to bridge the absence of feeding to only be three or should I put in a veggie slice or what?
<Skip the feeding block option; minimal benefit and they can mess up water chemistry as they dissolve.>
I'm sorry to bug you about something so specific, I wouldn't consider feeding them if it was three days, but with the ammonia issue in the back of my mind I'd like to maximize survival the best as I can. Haven't lost anyone yet.
<Indeed.>
And finally, what to do with these small snails and when to do it. Perhaps return them to the LFS when they are a big larger or are these tiny animals enough of a threat to this trip that they should be pulled out before then.
<Manual removal of the adults should prevent further generations. Otherwise let your Clea helena eat them, if you have some.>
peace
<Cheers, Neale.>
Re: Last Check before First Trip 5/11/10
Thank you for the ID on the snails. They do look like Physa but there are no adults.
<Eggs are common on plants.>
Well, I guess I shouldn't say that since I never heard of this species until 10 minutes ago.
<Well there you go.>
More reading to do! Unless they hitched inside the closed shells of the Nerites then it's either the snail fairy or both myself and the LFS need new glasses.
<Perhaps.>
Should I do an extra percentage of water change? 20%? 40%?
<Just do a regular water change. No need to complicate things. Cheers,
Neale.>
Re: Last Check before First Trip 5/11/10
Neale, if you see this before replying to the last one. Is this species of snail a nuisance?
<Physa spp. you mean?>
I mean is this a typical hitchhiker that one would otherwise not buy or want in the tank on purpose? So far I see that they are fast breeding.
<They may eat soft and tender plants, but I've never found them to be a particular problem. They prefer algae, and most of the time my specimens are either on the glass or on top of the floating plants. I consider them pretty harmless, but then I do have Clea helena, puffers, Synodontis or loaches in the tanks with them, so their populations are bound to be kept in check somewhat. Cheers, Neale.>

Snails, FW, control    7/31/09
Hello,
I have a number of small snails in my 20 gallon tank. They came in on a live plant and have multiplied like rabbits. I must admit they do seem to keep the tank clean. Is there an effective way to keep the population of snails in check? I'd like to have some, but not dozens and dozens.
Thanks,
Jon
<Snail populations grow fastest in tanks with lots or organic debris, so one way to control their population is to keep the tank (and the filter media) as clean as possible. Manually removing snails is an option too,
with various DIY traps described in books and web sites. JBL manufacture a device called the LimCollect that could be used if you want a commercial product. None of these traps works particularly well, and you have to use them night after night to have any hope of reducing a snail population.
Snail-killing potions should be avoided as these usually do more harm than good: a bunch of dead, rotting snails will do far more damage to your water quality than they would alive! My favourite way to control snails is to add a few Clea helena. These are snail-eating snails that, over time, have a remarkable impact on populations, removing most of the snails smaller than they are, so only a few larger ones survive. Cheers, Neale.>

Snails and Duckweed: FW Snail and Duckweed Control. Also Plant health. 7/23/2009 Dear Crew: <Hi Tricia.> First, I can only restate what so many others have said before - your website is awesome and absolutely my favorite browsing spot. Thank you again for all your hard work! <Thank you for the kind words.> I live in fear of repeating a silly question you have answered a thousand times before... but I cannot seem to find clear answers myself. Here goes... <Fire away.> I have a 30gallon planted freshwater tank. Fluorite substrate, 180gph power filter, 96watt Coralife lighting 6700 spectrum, temp at 78. I live in a hard water area and try to do as little "messing around" with my water as possible. Ammonia, nitrites at zero. Nitrates at 15ppm (in local water unfortunately). Ph 7.7, GH 22, KH 5. I add marine salt to raise density to about 1.004. <Sounds great. Thank you for these details.> Tank residents are 3 Sailfin mollies (1male, 2 females), 4 female swords, 2 Otos and 2 pygmy Corys (oh, and a random fry if the swords aren't hungry). All seem to be doing well. <Good.> My problem is with my plants. Most are doing fine. The anarchis (sp?) grows so fast that I trim it at least weekly. The Ludwigia looks spectacular and the Bacopa has doubled its original size. The swords are doing fine though not growing quite as fast - same for the Val.s. <Swords need a deep substrate or they get root-bound. You can try removing the swords, adding some more substrate in that area, and then replanting if you want them to take off.> But the Cabomba is horrible! It is dirty grey-green and shreds apart if I touch it. I am seriously considering just removing it as I would really love the real-estate to widen the Ludwigia patch. <Cabombas are touchy at best (I've never had luck with them) They like very calm water and specific water chemistry. The salt that you are adding for the Mollies is not likely helping either.> I also acquired (though I never intentionally ordered or placed) some floating duckweed. It grows like gangbusters. I like it - it is pretty and the fish seem to enjoy it. Just one problem - when the floating plants hit the current of the filters they get driven underwater. Most simply resurface a few inches away but some get tangled in... well in just about everything! <That sounds like duckweed.> After a day or two I can easily have duckweed nearly covering whole plants. <Not surprising.> I even find it "trapped" under the edges of the driftwood log. It is irritating and I worry, of course, about shading out my other plants. Is there some trick that I don't know to prevent this? <Aside from manual removal, not really I'm afraid.> I do not think I have too much current - there is very little agitation on the surface. I currently "scoop" duckweed out of the tank weekly and it seems to make only a small difference. Anyone want a few handfuls of duckweed? :) <hehehe.> My second question is about the growing cadre of snails in my tank. At first I diligently removed every one I could find. Then a brief algae problem convinced me to give them a reprieve. Now, algae is (praying hard here) under control and I don't think I "need" the snails. Apart from appearances, is there any good reason to remove them? <Assuming they are not damaging your plant, I wouldn't worry too much.> Do they cause trouble? <Some species can be destructive to plants, but based upon your comments, I don't think you are having that problem.> If I just leave them alone, exactly how many of these things will I eventually have?? <Snails turn waste food into more snails. As the food supply runs down (algae control) they will breed less frequently. Also, most snails lay their eggs above the waterline, so you can remove the eggs when you see them. You can read here for more information: http://www.wetwebmedia.com/fwsubwebindex/fwsnailcompfaqs.htm > Again, thank you so much for your site - I have spent many happy hours reading and learning! <My pleasure.> Tricia in PA <MikeV in FL> Re: Snails and Duckweed: FW Snail and Duckweed Control. Also Plant health. 7/24/2009 MikeV. <Hi Tricia.> Thank you for such a fast reply. If I may, a follow up or two? <Certainly.> I understand you to have said that there is no other control mechanism for duckweed other than "scooping and picking". <It is the only method that is safe for your plants and livestock.> Do many aquarists keep duckweed? <I know a few.> Would you suggest that I declare war on the duckweed? Or just keep blowing at it with my turkey baster and scooping out the excess? Could I even win such a war if declared? :) <That is a matter of personal preference. If you like how it looks and are willing to live with it, by all means keep it. If not, you can win the war by getting as much of it as you can out every day for a week or so.> As for the snails, I suspect that they arrived with some live plants and that their population soared when the algae did. Now that the tank is clean and clear... will they all die off at once and foul my water? <No, they are actually pretty effective when it comes to resource partitioning, they will just slow their breeding down.>> Will they begin munching on my plants (and with my luck, NOT the Cabomba that I don't like ...) <It is a possibility if they completely run out of food, but that isn't likely to happen.> Exactly how many snails are too many? <Hehehe... when you think you have too many.> Do I redeclare war? Selectively thin? Ignore completely? What is your recommendation? <If you think you have too many snails, I would selectively thin, This page: http://www.wetwebmedia.com/FWsubwebindex/fwsnails.htm  has an excellent method of "herding' them into one place, making them easy to remove.> Finally, I am having a hard time identifying the type of snail I have. Actually, I know I have a couple of tiny ramshorns. These others I am not so sure about. Could you look at these (terrible) pictures? <Actually, those pictures are quite nice.> Anything I need to know about them in particular? <It looks like you have both Nerite and Trumpet snails. The first 'in tank' picture is a trumpet snail. In your second picture, the trumpet snail is the one on the bottom, and the Nerite is on the top.> <You can read more about them specifically. here: http://www.wetwebmedia.com/FWsubwebindex/MollusksFW.htm/MalaysianSnailsF.htm http://www.wetwebmedia.com/FWsubwebindex/fwbrnerites.htm > And by the way, taking a close up of your tank is a great way to convince yourself to clean a bit more frequently! Yikes! <Hehehe, remember, a clean tank is not necessarily a sterile one.> Again, thanks SO much. My husband swears I spend as much time reading your website as talking to him! (You DO know considerably more about fish than he does... he likes his battered and fried with chips!) <Heheh, funny, my wife says the same thing about me.> Thank you in advance. <My pleasure as always.> Tricia in PA <MikeV in FL>

Snail Problem, comp., sel.    04/23/09
All,
I have been reading feverishly for the past night and day regarding how to safely remove snails from an aquarium. My problem is that all the snails I have seen are located in my sump/refugium.
<Nothing really wrong with that, is there? Marine aquarists go out of their way to put invertebrates in their refugia!>
My "specs":
75G FW with two Comet GF (6-8") and one Pleco (6-8"). Tank is heated/chilled (it's a hobby...) to around 75/76F.
<OK.>
I have a 20G sump/refugium with plants (Anacharis, if I remember correctly) that I purchased a few weeks ago, and this is likely where they came from. I thought they were clean, but I was obviously wrong. I have an Eheim 1262 pump in the refugium for return flow, and I need to know if the snails/eggs can transfer through the pump into the main tank? I have not noticed any snails in the main tank and boy did I look around hard last night after finding the snails in the sump. The sump has a 6" deep Seachem Fluorite
Black Sand substrate. Will the snails burrow into this?
<Some genera of snails are burrowers: Melanoides, Clea for example; others, like Physa and Pomacea aren't really burrowers much.>
I haven't noticed any, but then again, I might not be able to see them.
<Indeed.>
I've been reading that the "put-food-in-something-and-remove-in-a-day" method helps control population, and I will be doing this (cleaned salt shaker with algae wafers in there now) over the weekend as I am leaving on a trip tomorrow morning and won't be back until Monday night.
<Takes a long time to have much impact.>
However, I also know this won't kill/capture all of them, but merely maintain the population. Since I have the plants in the refugium, I'm concerned about them being eaten. I am also concerned that due to the large
amount of algae in the sump/refugium, I'm never going to catch the snails.
They don't seem to be concerned with the "free food" when they have all they can eat off the glass. Which brings me to more concerns, such as upsetting the balance I had with nitrates, and potentially getting into the main tank where I will most likely lose the war and have to restart the entire aquarium (something I'm not really wanting to do for obvious reasons and since I don't want to put the fish through the stress).
<Repeat after me: Snails are harmless. There is X amount of protein in your aquarium, and some goes into the fish, the rest into the snails and heterotrophic bacteria. The snail population expands to equal the amount of protein. Provided you don't overfeed the tank, the snail population CANNOT expand indefinitely. It reaches a level. In itself, all the snail population does is speed up the decay of organic matter into the ammonia that the nitrifying bacteria can use.>
I've also read that chemicals, like Had-A-Snail is a bad idea for the fish and possibly the plants.
<Yes.>
It especially says to "take care with catfish". Not something I'm willing to risk unless the experts (you) say it will be ok for my Pleco.
<Snail-killing potions do more harm than snails do! Think about what happens if you kill all the snails, and they rot away all at the same time!
Ammonia spikes galore!>
But, I've also read that Fluke tabs may solve the problem.
<Copper at least will kill all sorts of invertebrates, but it's also toxic to fish, some more than others. Catfish, loaches, Mormyrids, puffers are among the species most intolerant of copper.>
However, I can't tell from reading online and the manufacturer instructions how detrimental it will be to catfish and plants. This would obviously be the easy solution and I'd be happy to try it if you guys think it won't hurt any of my fish. I would take the fish out of the aquarium if I had another place to put them, but
all I have is a 10G tank I use if I ever have to move/do construction on the main tank. This is definitely not a suitable home for them for more than a day.
<Specific fluke medications other than copper will have little/no impact on snails.>
Another idea I read about, a loach, doesn't seem feasible as the environment just isn't suited for them. I'd hate to put a fish in a place that isn't suited for them just to help me out. No reason it has to suffer for my mistake.
<Quite.>
I was thinking the following in regards to killing the pests: Replace the sump for a couple of days with a canister filter I have and remove the water from the sump leaving it mostly exposed to air (the sand holds a good amount of water) and attempt to "dry out" the snails. Does this work? Will the snails die out of water?
<Some will, but others, such as Melanoides, can survive for months out of water in a hibernating state.>
Will they try to burrow into the sand?
<Some will, yes.>
If that isn't a good idea, what about mixing only the water in the sump with a large dose of aquarium salt? If I do this, will the sand absorb the salt?
<Melanoides can tolerate up to 50% seawater, so your plants and fish will die long before they will...>
Will the plants die if I leave them in there? I want to try to disinfect everything I can, so I'd attempt to leave pumps and heaters in the salt water if I did this.
Will this be fatal to the fish upon reinstalling the sump? I understand I can dilute, like a couple of 100% water changes, but I'm worried it will ruin the substrate which will kill the plants and harm my fish. I can't
find any of this information on your site. Surely I can't be the only one that ever had a sump infected with snails, but then again, maybe I'm one of the rare people running a sump on a FW tank?
<Snails aren't that big of a problem. Simply remove the surplus snails as you see them, but otherwise ignore, and instead control excess protein via better aquarium management.>
Help! And THANK YOU so much!
John
<Do see here for a useful snail-eating snail, Clea helena.
http://homepage.mac.com/nmonks/Projects/cleahelena.html
Widely sold in the UK at least, sometimes as the "assassin snail". Cheers,
Neale.>

Snails, FW, sel., contr.   09/08/07 Hi crew, The other day, Neale gave me some advice on keeping my sand 'safe' for my freshwater tank. It was suggested that Malayan livebearing snails would be good to keep the sand aerated and to eat debris, etc. It's just a small 6gal., and so far just two fish. So I've done some reading, but here's my questions. If I get the Malayan snails, seems they'll reproduce prolifically; will they eat up all the algae? I'm worried that my Otocinclus won't have enough to eat if this happened. Also, being that they would reproduce so much, do they contribute to the bio or waste load much; or is it negligible? Thought I'd ask since my tank's so small. Lastly, would the water condition needs differ much from the Oto? Thanks so much! Vanessa <Hello Vanessa, Malayan livebearing snails (Melanoides spp.) do have a bad reputation among some aquarists, while others consider them a blessing. I fall into the latter camp. Here's why. Melanoides turn organic material into snails. They don't eat gravel, they don't eat sand, and they don't eat live plants or fish, EVER. So if the Melanoides are multiplying, they only do so because there's "stuff" in the tank for them to eat. That might be uneaten food, it might be decaying plant leaves, it might be a dead fish, or it might be algae. Provided you keep the tank free of those things, the snails won't multiply very much because they can't. In a clean tank where all they have to eat is algae and tiny amounts of organic detritus, they just don't become a problem. They may be breeding, yes, but they're dying too, so you end up with a more or less steady population. It's in messy tanks where people have inadequate filtration and overfeed their fish and don't remove dead plant leaves that the snails become problematic. Even in large numbers though, they don't do any harm, and removing them isn't especially difficult. You can buy little snail traps for about $5-10 (it's called the JBL "Limcollect") and you could use one of these every six months or so if you thought things were getting out of hand. Some folks make their own lobster pot-type traps from small plastic cartons and the like. Since the snails crawl onto the glass at night, it isn't difficult just to turn the lights off early one night, and then wait for the snails to emerge, and then scrape them off with a net or suck them up with your siphon. It's no big deal. But really, I leave them to their own devices. No, they won't out-compete you algae-eating catfish, and no, they don't add much to bioload on the filter. On the plus side, they ensure there's no anaerobic decay in the tank and they help aerate (if that's the word) the substrate encouraging good plant growth in the same way earthworms do on land. They are also very good "early warning" monitors: if you see them on the glass in the daytime making a bee-line for the surface of the tank, it means you have a problem. As far as water chemistry goes, they're not fussy. In soft/acid water they tend to reproduce very slowly, which may or may not be a good thing depending on your needs. I'll also add that they are extremely pretty little animals. Take a look at one close-up: they have beautifully sculpted shells with red and purple markings. If they were rare and difficult to keep, aquarists would covet them... but because they're so easy to keep, we scorn them. Strange. I hope this helps, Neale.>

Persistent High Nitrite Level FW  1/31/06 I have read other messages on your site and other articles on other sites about high nitrite levels, but I still don't quite get it. I have a 10 gallon tank with 10 fish: 2 balloon belly mollies 2 ghost catfish 5 orange von Rio tetras 1 algae eater There are many, many small snails that were acquired accidentally with an aquatic plant that died some time ago. . . The snails, however, live on and reproduce at a staggering rate. <Mmm, you might want to collect and remove a bunch of these periodically... easy to draw to a small glass tray with a sinking bit of algae based food or blanched vegetable... as bait> Until today, I had a philodendron sticking out the top of the tank with its roots submerged. I took it out thinking that this was perhaps contributing to the problem. <Oh! Yes> About a week ago one of my mollies (there were three) started to act strangely as if she couldn't submerge. She would still eat when given food, but couldn't swim down to eat off the bottom like she always had. She had also lost a lot of weight. Eventually, she became very lethargic and got to the point where she was upside down and couldn't turn over. I took her and another sample of tank water to the local pet store. They said it didn't look like she had any disease and offered no explanation as to her condition. I assumed it was just old age and I only include this description in case it is symptomatic of some other problem. Anyway, when the girl at the store tested the water (something I had never done--shame on me), she said that the pH level was low and that I should increase it with a pH increaser. I bought the pH increaser and a test kit that tests for NO3, NO2, GH, KH, and pH. When I got home, I did a 30% water change and added 1 tsp of salt, which is my normal routine. (I keep around 3 tsp of salt in the water at all times.) I did not add any pH increaser. I tested the water immediately afterward and it looked OK except the water was hard, so I added a teaspoon of salt. The next day, however, the levels were as follows: NO3 = 40 <I'd keep this under 20 ppm> NO2 = 1.0 <Dangerous... should be zip, nada, zilch> GH = 300 KH = 0 pH = 6.8 I added another teaspoon of salt and changed the filter which was very dirty (because I had made the water very silty the last time I changed it--explanation below). The next day, the nitrite level was at 3.0. <Yeeikes!> I did another 30% change and waited an hour before testing. The nitrite had gone down to 1.0. One day later, it was back up to 3.0. The next day, 3.0 again. The following day, 5.0. Today, it was still 5.0 so I did another 30% water change. One hour later, the levels are as follows: NO3 = 40 NO2 = 3.0 GH = 150 KH = 40 pH = 7.2 There is currently about 8 teaspoons of salt in the water. <Mmm, you might want to mix some of this salt up in tapwater and test it for nitrite...> The strange thing (to me) is that the fish seem to be happy and healthy. From everything I have read in the past few days, a 5.0 nitrite level should have them dropping like flies! <Let's see... luckily your pH is low... if it were a little higher, the nitrite would be MUCH more toxic> I have checked for brown coloring of the gills and see none. They are not gasping for air at the top of the tank either. I can only surmise from what I have read that the salt is keeping the nitrite from being as toxic as it otherwise could be. <Oh, yes... this also> I have noticed the mollies scraping themselves occasionally on a structure in the tank. I read today that this was one sign of nitrite poisoning. I have had this tank for 8 months now and only three fish have died in that time (except for the batch I introduced right at the beginning before the tank had cycled!). About a month ago, I did a very thorough cleaning of the tank. I really stirred up the waste on the bottom, trying to get as much out as possible. I took out all the structures and washed them with hot (not soapy) water. I changed the filter as well. I also started feeding them much more around that time. Basically, I unwittingly did everything I could to raise the nitrite level! My questions are this: 1. Why isn't the level decreasing? <I suspect the houseplant> 2. Why are the fish still alive and acting normal? <They're tough, adapted to it, and the salt> 3. I have read on some sites of a biological filter or a biofilter: Is this (a) just another name for the normal filter, <Mmm, of a sort... all filters are ultimately biological to degrees> (b) a different kind of filter that I should have, or (c) just a term that refers to the nitrogen cycle that occurs within the tank? <Mostly the latter> 4. Could the snails be causing problems? <Yes... carry disease... and can influence water quality in high numbers> 5. I have read that most of the bacteria live on the filter. Wouldn't changing the filter then lead to these levels getting all out of whack every time? <Yes... a common problem/occurrence. In established systems not such an issue> Thank you for any help you can provide. - Bryan <I would read over WWM re FW filtration, add more filtration, remove the houseplant, reduce the number of snails, test the salt... Bob Fenner> Re: Persistent High Nitrite Level... Betta systems and snail removal technique  2/3/06 Thank you. After removing the philodendron, the nitrite levels immediately dropped and are now < 0.5 ppm. Other levels are beginning to even out as well. <Ah, good> I thought you also might like to know that I have rigged up a plastic fork on some fishing line as a snail remover. I stick a piece of vegetable on the tines of the fork, and when a few snails crawl on, I hoist it up and scrape them off. It's not pretty, but it's been fairly effective! <Neat! Bob Fenner>