Opinion on Chemical Media in Planted Aquarium  2/4/08
Hi -
I wanted to get the expert's opinion on chemical media containing carbon with ion exchange media (such as Chemi-Pure and BioChemZorb) and the planted tank. My fear would be scavenging too many trace elements and hurting the growth of my plants.
I've used Purigen with great success, but have heard various rave reviews of the Chemi-Pure, and - to a less extent - BioChemZorb.
Thanks in advance for your feedback. Your site is, by far, the definitive online guide for fishkeeping.
Very truly yours,
Stu
<Greetings. I'm not a big fan of carbon in freshwater tanks. It does nothing that regular water changes don't do better. Carbon was most valued in the Stone Age of the hobby, where people deliberately avoiding changing the water. 10% a month was normal. The idea was "old water" was better than "new water". The big problem with old water is that organic decay in the tank produces organic acids that lower pH and turn the water yellow. Carbon adsorbs organic compounds, and by using carbon in a filter, the aquarist could keep the pH stable and the water clear. Nowadays we routinely change 25-50% of the water per week, so the dissolved organic compounds in the aquarium never reach a concentration where they are sufficient to cause harm. In terms of value, biological and mechanical filter media deliver more tangible results per cubic centimetre of filter space, and chemical media for buffering water chemistry can also be useful under certain circumstances. Finally, the active life of carbon (regardless of how it is packaged or what brand it is sold under) is literally a matter of days. One manufacturer of fish medications makes the point that carbon over 5 days old won't have any impact on their medication because it won't absorb sufficient quantity of that medication to affect the efficacy of the drug involved. That pretty much sets it out for you in terms of how often carbon needs to be replaced if it is to do any good. Carbon doesn't removed many inorganic substances, iodine is the only one of note, if I recall correctly. So carbon won't really do anything to the CO2, iron, magnesium, etc. that you need to keep plants healthy. The minerals at least need to be in their reduced rather than oxidised state, so won't be in the (oxygen-rich) water anyway but in the (oxygen-poor) substrate. The carbon obviously doesn't do anything to the substrate. So bottom line, in my opinion, is buy whichever you want since they're all a waste of money and don't make any difference in the big picture. Cheers, Neale.>

Platy companions, filter maintenance  – 1/18/08
hi there,
I've written to you before and got good advice,
<Good oh.>
what I am wondering is, when I'm changing the filter sponges, which ones can I just rinse through and which ones do I have to replace completely?
<Ideally rinse them ALL in buckets of aquarium water, and never replace more than 50% of the filter media in any one go. Typically the mechanical media (the coarse sponges in your system) will need to be cleaned more thoroughly, and perhaps replaced more frequently, than the biological media (the finer sponges). Juwel filters also have little white cotton pads you stick at the very top of the system to trap big bits of waste, like dead leaves. These can be replaced as often as you want. I find it cheaper to rinse them off every week or two rather than replace them every month or so. But it doesn't matter much.>
I have a Juwel Rekord 70. also which fish would be good tank companions with platy? I was going for Neons next, my tank is up and running about 7 weeks.
<Platies are hard water fish, and for that reason your best bet is to mix them with other hard water fish. That way you can tweak water chemistry, or use salt as a therapy, without worrying. Other livebearers are ideal, but so are rainbowfish and halfbeaks. If your water quality is good, then certain dwarf Tanganyikan shell-dwelling cichlids can work well at the bottom of the tank. They work surprisingly well with livebearers.>
thanks again!!
David.
Davy-D-
<David, please please please use the Shift key next time to put capital letters where they belong! The idea behind this site is that the questions we answer are available for others to read, not just you, and letters without capital letters are difficult to read. This is especially true for those who don't read English as their native language. Thanks! Neale.>

Filtration help... FW set up Qs, learning to read/use WWM   12/18/07
Hi there, first I just want to say how much I appreciate the staff there who run this site and answer questions so fast. you guys are great and have helped me so much with my learning process, keep it up!
Now, I have an established 10 gallon tank and am wanting to setup my 30 gallon and 5 gallon tanks (haha Multiple tank syndrome!). The 10 g has a small AquaClear filter on it currently. Yesterday I added the large AquaClear filter and a small sponge filter to the 10g to try to get the media colonized with bacteria.
My questions are: How long do I have to leave the new filters on the established tank for it to be colonized so that its good to go on the new tanks?
<Read here: http://wetwebmedia.com/FWSubWebIndex/fwestcycling.htm
and the linked files above>
I would like to get this on my new tank as fast as possible so I can put Bolivian rams in it...(long story I know they should be put in last, but where I live they never usually come here and they have been sitting in the store for 3 weeks and I wanted to get them before someone else snags them).
<Can be "goosed"...>
Also there is much happening in my 10g right now, with all the bubbles and movement, 1 of my baby panda cories got sucked into the uptake tube last night (I was sooooooo sad/mad...I'm getting so attached to them!) and it died. I feel terrible that it must have died a slow and painful death. The other fish (3 baby pandas, 4 tetras, 2 harlequins) don't look too happy right now, I had to change around the decor a lot..I just put nylon to cover the large filters uptake tube but will this interfere with the colonization process?
<No>
Is it possible to have TOO much oxygen or movement in a tank?
<Not practically>
Also the sponge filtration unit is meant to eventually go on a 5 gallon with a Betta, it seems quite noisy and bubbly.. will the Betta be ok with it?
<Likely so>
What I did was I tied 2 knots into the tubing to slow the rate of air coming out of the pump, will this wreck the pump due to backflow?
<Back pressure? Perhaps shorten its effective "life">
Finally my last set of questions...I bought a bunch of driftwood to put into each tank.. about 1-2 pieces each.. I bought them to soften the water a bit since water is very hard here. I don't want to boil them because I want them to leach tannins, is this ok, can I just soak them?
<Can>
How long should I soak the pieces for?
<Read here: http://wetwebmedia.com/FWSubWebIndex/rkwduseaq.htm
and the linked...>
Is there such thing as too much driftwood?
<Yes>
I don't know my water hardness but I know its very hard. How long will it take for the tannin levels to be established...what I mean is do I have to constantly monitor pH, or say after 1 month that pH that its at it will stay there?
<See WWM re FW pH...>
Sorry I hope it makes sense. I take out the carbon to have the tannins in the water, is this correct or do I leave the carbon in?
thank you so much!
<Read on... RMF>

FW Fluidized bed filter question, Loricariid sel.  - 12/13/07
Considering a fluidized bed filter as alternative to bio balls from sump on 120g planted freshwater tank (rainbows and Plecos). 2 questions - Is there any value to sizing up on filter...it is only $10 more to go from 300g to 600g to 900g. Ignoring size limitations on height, is there any reason to not get a bigger one - unnecessary overkill?
<No real functional advantage... perhaps some disadvantage in electrical costs to push water through a larger unit>
second, re: Plecos, I plan on having the following...any Compatibility problems (I searched PlanetCatfish and can't really find the info): gold nugget, queen arabesque, royal, blue phantom, maybe a zebra. I also have a striped Raphael. Only one of each. Any issues?
thanks
<Mmm... well... not compatibility... but the smaller Loricariids are more social... I'd likely get more than one of these. Bob Fenner>
Paul

Two questions... platy repro., filtration maint.   10/16/07
I have a 10 gallon freshwater tank at school with 2 platys (male and female) and one fry that is about 1 cm long now. I found the fry during a water change about 2 weeks ago and have him in one of those breeder nets in the tank. It has been so much fun seeing him grow from just a speck to where he is now. When should I put him in the main tank with the other two platys?
<When its big enough not to be eaten! At a couple of months should be fine.>
Also, how do you know when to change the filter?
<Ideally, never. You clean the filter, yes, but that's nothing more than rinsing filter media in a bucket of aquarium water (not under the tap, as the chlorine can kill the bacteria). When you've washed out the worst of the sponges (or whatever), put them back in the filter. Only if the filter media is completely blocked up should they be replaced, and even then, no more than 50% of the media per three months.>
My filter is one that hangs on the side. I've had the tank running for about two months now. Should I put a new filter in some old tank water so that the good bacteria can start getting on it?
<The water carries virtually no filter bacteria, so what you suggest is a complete waste of time. Instead, avoiding changing too much filter media at once, and let the mature media colonise the new stuff.>
Thanks!
Carolyn
<Good luck, Neale>

Using a brand new filter on a seasoned tank 10/3/07
HI,
<Hello,>
I have a 75 gallon tank. I had a Eheim Filter that just decided to not run correctly no matter what we do new parts etc....
<Too bad.>
I went and got a new Fluval filter last night. The place I bought the filter told me to keep both filters running for about two weeks to get the bacteria into the new filter before I stop running the old filter.
<Not the way I'd solve this problem. Much easier to simply take all the mature media from the old Eheim and put them into the new Fluval. Problem solved.>
The problem is the old filter is blowing air, lots of air. It will run ok for 1/2 hour or so and then a big burst of air comes out in to the tank and needles to say a lot of micro bubbles with it.
<Ah, seen this happen. It usually isn't the filter per se, but how the filter is set up. Air (obviously) can't magically get into a watertight filter. But if you configure the inlet (the "sucking" pipe) somewhere that gets air bubbles, those air bubbles get sucked into the filter. Certain canister filter designs don't handle this problem well, and the air bubbles collect at the top of the canister, often around the impeller (the spinning blades). Eventually the top of the filter gets so full of bubbles that some bubbles break away and go into the outlet stream of water. There's usually a lot of rattling noise as well. Anyway, the solution is to re-jig the position of the filter inlet. You also need to take great care you are reassembling the filter properly, such that you aren't trapping air inside the canister to begin with.>
It is stressing the fish out, they run for their lives (so to speak) when this happens. Last night I had both filters running but the fish started to stress out swimming fast and changing color etc.....
<Hmm. Can't really imagine it's doing them much harm. Compared with, say, heavy rain or ocean waves, a filter blowing bubbles is pretty trivial.>
My question is, is it ok to just run the new filter alone, is there anything I should do to the filter, what is the correct thing to do.
<As above, take the media from the old filter and install in the new.>
I have both filters off right now,
<No! Never, ever switch off a filter. Anything more than, say 20 minutes, can kill the bacteria.>
also could the fish have stressed out do to the two filters running could this be to much filtration for a 75 gallon tank at one time.
<Not a problem. Aquarium fish will tolerate as much as 10 times the volume of the water in turnover per hour. It is very difficult to have too much filtration. Compared with the flow of a river, filters are insipid trickles.>
The fish were so stressed that I have both filters off right now and this calmed them down.
<They get used to it. My freshwater tank has ~10 the volume of the tank in turnover per hour. It took the fish an hour or so to get used to the extra water movement when I installed the third filter, but they're fine now.>
I will wait for your response until I do anything with the filter. Thanks in advance for your help.
Deb
<Hope this helps, Neale>

Filters and pH questions 9/26/07
Our tap water here in Oregon is very very soft (dH 2-3), but they use sodium hydroxide to raise the pH to 7.7 so as not to rust pipes.
<What a horrible set of water conditions... very soft, but slightly alkaline. Nothing much really likes these conditions.>
It quickly drops to 7.2 or so in the tank.
<Well that's lucky.>
Is this OK for cardinal tetras, Apistogramma, loricariids? Soft water Amazon fish seem to be doing well.
<I'd be tempted to add a certain amount of a pH-down product to reduce the pH to exactly 7, while increasing its buffering capacity. On its own, very soft water tends to fluctuate in pH quite a lot. This is not good. Standard pH-down products (usually sold as bottles, and you add a bit to each bucket of water just like dechlorinator) stabilizes the pH at some value. In hard water they're a bit of a waste of time and money, but in very soft water such buffering solutions (as they're called) can be very helpful.>
Also, I have a Rena Filstar filter. Has the standard 2 layers of foam, a bag of carbon (bio chem zorb) and a layer of micro fleece pads. Was thinking of replacing either one of the layers of foam or the carbon with either some ceramic biomedia or keta peat nuggets.
<Bin the carbon. Total waste of space. In very soft water, the filter bacteria tend to be less happy than in hard water (they like hard, alkaline water best of all, and stop working completely below pH 6). So concentrate on adding as much biological media as possible to get the best water quality. Choose whatever according to your budget and preferences. The main thing is that the filter should have not less than 4x the volume of the tank in turnover per hour. In other words, for a 100 litre tank, the filter must have a turnover of 400 litres per hour.>
That's a lot of foam sponge, and maybe the carbon is not so necessary. The peat would lower that NaOH induced pH.
<Don't use peat. Peat is wonderful stuff in aquaria if you know precisely and absolutely what you're doing. But peat can rapidly change the pH and its results are completely unpredictable. In very soft water with practically zero buffering capacity, you could easily drop the pH from 7.2 to 6.0 overnight if you added too much, and this would kill your fish. Instead, use the buffering solution mentioned above, following the instructions on the bottle, and performing pH tests every day or two at first until you get a sense of how pH varies in the tank. What you're after is 7.0 day in, day out.>
What do you think?
<Messing with pH is something a lot of aquarists get into trouble over. There's a very good argument for not thinking about pH at all, and focusing instead on general and carbonate hardness. Both of these have a much bigger impact on the fish. With your very soft water, the KH value is likely to be very low, and as a result water chemistry stability practically non-existent. So your job is to stabilise water chemistry. Adding buffering solutions to the water will do this. This becomes more important the more fish you add, because the loading of the tank is positively correlated to water chemistry stability as well. In other words, heavily stocked tanks experience a drop in pH more quickly than the same tank would if lightly stocked (a process called acidification). So, move slowly, research the water chemistry topics here at WWM, and measure pH regularly to check that acidification isn't getting serious. Cheers, Neale>

Supplemental Filter - Freshwater   9/11/07 
Hi there Neale,
<Hello Lisa,>
I've switched three of my tanks over to black sand substrate - I love it and it no longer poses a problem for the catfishes' barbels. However since the fishes' solid waste doesn't sink through the gravel anymore, it is in plain site and the canister filter's intake won't pull the waste into the filter.
<This happens. Of course, all that gunk went into the gravel before, too, so the problem is only that you *see* the stuff rather than it wasn't there before. My tip is to [a] adjust the water flow and the slope of the sand to push the gunk towards one corer; and [b] simply use a siphon to remove the stuff when it gets too unsightly.>
I'd very much like to install some in-tank supplemental filtering and simultaneously add some additional bio media and water flow to remove any dead spots. I've been looking at sponge filters however I've noted that these are used for tanks with no substrate (and especially for fry). There are also some small corner filters - both small enclosed plastic boxes run by an air pump (that I used when I was a kid!) and exposed cushion type that affixes to the tank glass.
<Both these are EXCELLENT for biological filtration, but less so for mechanical filtration. You might actually find a powerhead or an airstone would do a better job of creating water current, and so help the gunk get pushed around. It's only when it's the water column, as opposed to sitting on the sand, that the canister filter gets a chance to slurp it up.>
What would you recommend in this case please? I have one tank set up with a powerhead and quick filter however was looking for something a bit less obvious for the other (smaller) tanks if possible...
<I suspect that even if I recommended stuff, in a small tank, it would be either cost prohibitive or else just disappointing. In a small, not too heavily stocked tank, you would probably find a plain old turkey baster a better investment. (Second time I've recommended these tonight. Odd.) Adjust the sand as mentioned before so one corner (at the front) is lower than the three others. Adjust the filter so it pushes water about such that the gunk collects in one corner. There's some trial and error involved here, obviously. Once it works, you'll find all the waste sitting in this corner. Whenever it becomes too unsightly, you whip out the turkey baster, suck out the gunk, and throw the waste into a pot plant where it can do some good (excellent organic fertiliser!). No fuss, no muss. Since you're going to be doing water changes every week or two, the turkey baster tends to work perfectly well as a spot cleaner the rest of the time. Given a turkey baster only costs a couple of bucks, it's a cheap solution, too. There's also great for moving fry, dishing out live food, feeding invertebrates, separating dwarf mouthbrooding cichlids from the their fry... so many things!>
Thank you very much!!
Lisa
<Hope this helps, Neale>

Auxiliary filtration, FW     – 06/27/07
Hi Crew!
<<Good afternoon. Tom with you.>>
I am upgrading from my 55 gallon FW tank to a 90 gallon.
<<Congratulations!>>
I plan to use my Eheim 2026 (rated up to 92 gallons). Would an Emperor 400 be a good choice for supplemental filtration in the larger tank?
<<I’m running an Emperor 280 along with a Fluval canister filter on one of my tanks (50-gallon) and like the filter just fine. I’d heard reports from some folks that they found the filter to be “noisy” particularly when evaporation drops the water level somewhat. I’ve not found this to be the case but, then, I don’t let my water level drop excessively, either. The Emperor units, as you’re no doubt aware, come with two filter “cartridges” (four on the 400 model) along with the bio-wheel(s). The lead cartridge has a polyfiber pad attached to the plastic container which is filled – somewhat – with Black Diamond activated carbon. This is the “use and toss” cartridge. The second is of like-construction but can be opened and filled with whatever your media of choice might be. I like the polyfiber pad on the first cartridge for a little extra “polishing” of the water but the carbon is unnecessary, for the most part. The recommended change interval on this cartridge is 2-4 weeks. Replacements are cheap enough so it kind of comes down to your own call, the pros and cons of using carbon media in FW filters notwithstanding. Bottom line? I’d do it if it were me.>>
I plan to make it a planted discus tank.
<<Another good reason to go with the Emperor. I’ve found that the design of the filter is such that there isn’t a lot of current/disruption created by the output. Something that your Discus – if they could – would thank you for.>>
Thanks in advance for your reply.
<<If you haven’t done this already, check out the articles on our site written by Alesia Benedict for “Conscientious Aquarist”. These deal, very specifically, with planted Discus tanks and are a joy to read as well as being very informative. Best of luck in your venture. Tom>>

Under ground filtration with a canister filter - 06/27/07
Hey!
<I really, REALLY don't like "hey" as a greeting. Is this a common salutation in America? In England, it would be considered very rude -- as in "hey you, grotty little poor person who's name I can't be bothered to remember"...>
I must say that I have found your website very helpful!
<Cool.>
I have a 125gal set up with an under gravel filter at the moment. It worked fine as long as my fish population was small, but I now want to increase my filtration.
<Typically, undergravel filters work fine until a tank is overstocked, at least where small community-type fishes like barbs and tetras are concerned. Just like any other filter, if you dramatically increase the number of fish, it takes some weeks for the undergravel filter to "scale up" in response. So during this phase, keep an eye on nitrite and/or ammonia levels.>
I want to go to a canister filter (Eheim pro 2 or 3). Should I draw the suction through my under gravel filter or should I remove the under gravel filter and just pull from the tank?
<The best of both worlds is a reverse flow system. Here, water is sucked into the canister filter, and then pushed outwards into the undergravel filter so the water emerges back into the tank upwards through the gravel. Why this works well is that it uses the canister filter to mechanically treat the water, removing solid wastes, and only clear water gets pushed into the gravel where bacteria remove the ammonia and nitrite. Because water is rising through the gravel, it pushes out solid waste, stopping the gravel from getting clogged, improving its performance and also making it much easier to maintain.>
Is one situation better than the other? Why?
<Explained the best system above.>
I also have a few (two or three) plantings in the tank and I have been told that the under gravel filter is detrimental to their growth. What is your opinion on this?
<It depends on the plants. Plants without roots, like Anubias and Java fern, couldn't care less. But plants that rely on their roots to extract minerals from the substrate do indeed grow better without undergravel filters. This isn't to say you can't grow plants in tanks with undergravel filters, you can, it's just they don't do very well. You're also limited to the hardier species, and will need to take extra care to put fertiliser tablets close to their roots periodically. In a tank with an undergravel filter it is simply easier and more reliable to skip plants or go with species that don't have roots. Anubias, Java fern, Java moss, floating plants, and things like Elodea that have midwater roots are the way to go.>
They are mainly for snacking in between meals by the veggie eating fish, but I would like to grow a bit more if possible.
<Growing plants in tanks with vegetarian fish is a bit of waste of time unless you choose inedible species such as Java fern and Java moss. Anubias sometimes does well, but herbivorous plecs rasp it away to nothing.>
Thanks for all your help.
Ed
<Cheers, Neale>

Used SeaClear Aquarium-poor choice? For FW...  6/5/07
Hi,
I have researched these questions on your site and can't find the answers, so am writing to you. I am new to your website; just discovered it yesterday, 2 days after buying a used (10-11 years) SeaClear Eclipse 2, Clarity Plus 75 g. tank. I had set my heart on a Tenecor; it looked like the best quality, but then I saw this ad and it sounded really good, with a beautiful hand-made large cabinet and hood all for $400.
<Both companies make good products in my estimation. If the used one has been not abused, it is likely fine>
I researched it for 3 or 4 days, but now after poring over your website for 2 days, it looks like it might have been a poor choice.
<Well... the "Eclipse" line I am definitely not a fan of... but the "built-in" filtration back can be supplemented, or best even ignored...>
Anyway, it's been set up for 2 days now and things are going well; the fish are very happy, since they outgrew their old tank (35g.) I have only 6 fish in it; 3 Pink Kissers (6-7 in.)
<Nice!>
, a Pleco (14")
<Yowzah!>
and 2 Clown Loaches, (3"). I've had aquariums for 40 years, but nothing over 35 gallons. The tank is beautiful, but now I find out the truth, that filters for a 48 x 18 x 24" tank are ridiculously pricey: $50 to $60!
<Heeee! And there's electricity to run them... and replacement media!>
Where can I get cheaper prefilters, or can I make them?
<Mmm... if you're handy... there are DIY varieties... but really... Unless you have plenty of spare time, the commercially made ones are superior>
I live in a rural area with no LFS, but I have catalogs from That Fish Place and Drs. Foster & Smith,
<Both mighty fine companies as well>
so is there something I can order from them to substitute?
<For? Do try a search on WWM, using the cached-view version here: http://www.wetwebmedia.com/WWMAdminSubWebIndex/question_page.htm
with the terms "SeaClear", and "Eclipse"... read the modifications proposed...>
The rest of the filter is the bioballs and the pump, in other words, the original system.
<Is ridiculously inefficient by itself... and a pain in the keester to try to work on>
The previous owner was very happy with it for 10 years.
<Right... that's why they sold it for so little...>
What can I add to the filtration to make this a better tank?
<As stated... seek per above... I myself would drill the back, make the filtration in a tied-in sump below likely... pump the water back from there to the main tank...>
It looks great right now. Also, after it is established, I would like to add another Kisser, 2 more clown loaches and maybe a small school of tetras or
rasboras. Will this work?
<Maybe... take care with the new Kissers... they're going to look/be tiny compared to your present ones... may be chased mercilessly... and DO quarantine all new/incoming livestock... Likely about the last thing you want is to introduce a pathogen here...>
I feel like a novice after looking at the expertise on your site. Thanks, Carol M. ;<)
<Heeee! Keep looking... you'll be one of us soon! Cheers, Bob Fenner>

How often should filter cartridges be cleaned/replaced – 05/21/07
Dear Crew,
<Nicole.>
I have what is likely a silly question about filtration, but I've been puzzling on it for a while and I can't seem to figure it out.  I have a 10 gal tank with a Tetra Whisper Power filter, and my question is this:  the manufacturer's instructions suggest changing the cartridges once per month, but if I throw out the cartridge, won't I be throwing out the beneficial bacteria that are growing on it? <You are right.>
How long will it take the bacteria to re-establish themselves in the new cartridge <A few days, many will be left in the substrate and on the decorations.>, and will this be harmful to the stability of my tank? <It could, if you’d also clean decorations and substrate.> Should I just be rinsing the cartridges out <Yes, just rinse the cartridges as soon as you recognize water flow to become significantly weaker or when water just overflows the tube like chamber. Those cotton or foam like materials can last for several years, only wool in other models needs to be replaced more often.> and replacing the carbon instead of changing them every month? <You do not need to use carbon at all. New activated carbon will only be good for one or two weeks. It’s only useful in specific cases e.g. to help removing some chemicals such as remedies or certain toxins. It needs to be introduced fresh to your filter in such cases.>
Thanks in advance for your help, my tank is going along so well and I just don't want to mess it up! Nicole. <You are welcome. Have fun with your tank. Marco.>

Too much Filtration? FW   5/11/07
Dear Crew Members,
<Hello Anna>
Is there such a thing as too much filtration?
<Yes and no. Yes, you can have too much water movement, and if there is too much turbulence and the water becomes super-saturated with oxygen, tiny gas bubbles can cause serious problems. But no, you can never make the water too clean, because by any practical standard the conditions in an aquarium will usually be poorer than most "wild" environments in terms of water quality and density of livestock.>
I have a 55 gallon freshwater community tank. It has a wet/dry filter roughly 20 gallons I think and double BioWheel ( two BioWheel filters on either side of the intake).
<Do you mean the filter is rated for a 20 gallon tank? Obviously inadequate for a 55 gallon tank, assuming you have an average level of stocking.>
I also have a large protein skimmer.
<Which probably won't work in a freshwater tank.>
The tank is planted and will be home to mollies and other tropical fish under 4 inches of adult length.
<Do bear in mind mollies don't like the same water conditions as most tropical fish. At the very least they need hard (20-30 dH) alkaline (pH 7.5-8) water with practically zero nitrate (difficult to get in densely stocked aquaria). If you can't maintain those conditions, switching to brackish water (around 10-25% seawater salinity) helps keep mollies healthy, but the range of salt-tolerant freshwater fish is relatively small.>
I don't have any fish right now. Is there anything that is redundant or unnecessary?
<Personally, if you have your heart set on mollies, I'd go for a brackish water set-up and keep brackish water or salt-tolerant fishes such as gobies, glassfish, certain cichlids, certain catfish, sleepers, livebearers, etc. If you want a planted tank, skip the mollies in favour of platies or swordtails, both of which do much better under "normal" conditions than mollies.>
Thank you, Anna
<Cheers, Neale>