By Richard Lunsford

            After appropriate housing, temperature and diet, filtration is the next prime concern in an aquatic or semi-aquatic turtle’s long-term well-being. The same basic water chemistry concerns apply to turtles as fish, but turtles require stronger filtration. I’ll break down filtration per this outline: 

I.)   What is Aquarium Filtration? 

II.)   Filtration Capacity Principles for Turtles. 

III.)   Filter Media – what it is, what it does. 

IV.)   Overview of Popular Filter Models & Strategies. 

V.)   What is a Wet/Dry Filter? 

VI.)   Can I get rid of Nitrate without Water Changes? 

VII.)   Water Changes – Why Bother? 

VIII.)   What Test Kits do I need? 

IX.)   Pre-filtering. 

X.)   Safety. 

XI.)   Where To Buy.


I.) What is Aquarium Filtration?

It’s a 3-part System:

1.)   Mechanical – removal of particulate matter from the water (i.e.: crud, turds, uneaten food, etc). This matter builds up on the mechanical filter media (sponge, filter floss, etc) and is removed from the tank when you remove the mechanical filter media from the tank & clean or replace it. This is the type of filtration most people are familiar with, since it makes the water LOOK clean. It ranks second in importance. Note: mechanical filtration is easier if you don’t have gravel in your tank (the bare-bottom tank approach).

2.)  Chemical – the use of chemical media in the filter to remove unwanted dissolved substances from the water. The most common example is activated carbon. Some organic compounds bind to activated carbon (this is called adsorption, not absorption, since they don’t enter the carbon) – this can make the water look ‘sharper’ and reduce unpleasant smells, but it’s a luxury. Activated carbon can remove some medications and tannins (coloring agents released into water if you use peat in the tank). Another example is ammonia remover, which removes ammonia from the tank (until the media’s full & must be replaced) but can interfere with biological cycling. The common thread across chemical filtration is it uses media that are fairly expensive, have to be replaced fairly often, & most chemical filtration is unnecessary although it can be a luxury. Ranks 3’rd in importance.

3.)  Biological - #1 Important filtration system in your tank, & the one more people are ignorant of. Aquatic turtles (and fish, snails, etc) produce nitrogenous wastes in their bodies, and excrete part of it as ammonia, which builds up rapidly & is very toxic. Beneficial bacterial colonies (Nitrosomonas) grow on your filter’s biological media (Biowheel, BioMax ceramic rings, Aquaclear sponge, etc) that break this ammonia down into nitrite. Nitrite is also quite toxic. A second type of bacteria (Nitrobacter) grows on the media that converts Nitrite into Nitrate, which is only toxic at high levels. Nitrate is part of what you dilute when you do water changes in your aquarium. Biological filtration & the need to keep your bacteria alive is why your filter must run 24/7, and why during the first 4-6 weeks (while the bacterial colonies slowly develop) you must change your tank water at least once per week!!! Some try to jumpstart bacterial colonization with store products like Cycle; you may get mixed results. By all means try it, but test for ammonia & nitrite to see if it ‘took. For tips on jump starting cycling, keep reading!

Bottom line: Biological filtration capacity is your number one concern (due to the nitrogen cycle). Mechanical is useful. Chemical is a luxury, although activated carbon is a great last resort of ‘swamp smell’ proves a problem.

II.) Filtration Capacity Principles for Turtles.

            Choosing filtration capacity for anything is an inexact science. Your need depends on tank size, how many turtles and tank mates are in it, how much and what you feed, and whether you feed in the tank or a separate container, etc… Many people feed their turtles in a separate container (like a Rubbermaid tub); not only does this cut down on rotting food scraps and juices in the tank, but turtles often poop shortly after eating, and will do so in the tub. Some feed in a separate container, some don’t – see what works for you.

            My rule of thumb is arrange filtration rated for a tank 2 - 3 times the size of what the turtles are in. Do NOT factor in only having the tank partially filled; a half-filled 20 gallon tank should get a filter rated for a 60 gallon tank, not a 30 gallon. This assumes a ‘turtle load’ of about 3 turtles up to a year old in a 20 gallon long, perhaps 3 adult male basking turtles in a 75 gallon tank, etc… If you have a 75 gallon tank with one basking turtle, a filter rated for a 75 gallon tank might do although I’d still aim for twice. Factor in tank mates; fish enthusiasts recommend an adult Oscar should have a 55 gallon tank BY ITSELF, and 2 Oscars should have a 75 gallon tank alone. Adult goldfish have a 20-30 gallon/apiece need. Smaller tank mates don’t require so much, but they DO matter.

Remember it takes 4-6 weeks to build up bacterial colonies, so make sure you do a large water change AT LEAST weekly until your tank cycles. You will see for sale products like Cycle that purport to dump reams of beneficial bacteria into your tank. Feel free to try, but I've heard mixed reports so don't assume it worked without testing ammonia & nitrite days afterward. A great technique to speed cycling is to 'seed' your new filter with biomedia from an old one. If you have a Fluval 304 on an old tank, and you're putting a Fluval 404 on a new tank, put some Bio-Max ceramic rings from the 304 in a media chamber of the 404. THAT will jumpstart things a lot. Better yet, put an established filter from another tank on the new tank.

            On large tanks (55 gallon & up) consider using 2 filters; this spreads out the intake and outflow a bit, and if one filter breaks, you don’t loose all your bacterial colonies.

            Put intake and outflow lines at opposite ends of the tank; this helps ensure your filter filters all the water, without ‘dead pockets.’

Turtles are more resistant to bad water than fish. That's why quite a few turtle keepers don't know much about cycling; they never had all their turtles floating belly up from ammonia like fish keepers do. Some turtles are unusually sensitive to poor water quality (i.e.: map turtle, soft-shell turtles & the exotic Fly River Turtle). And I have read about high ammonia levels irritating turtles’ eyes. Remember: the smell of ammonia is used as an irritant to rouse unconscious people. That should tell you something about how it feels on mucous membranes!

III.) Filter Media – what it is, what it does.

Media type - depends on filter & purpose. Different brands of filter may use different media for the same purpose (for example, for biological filtration, Aquaclear filters use a sponge, Fluvals use porous hollow ceramic cylinders called Bio-Max and Magnum filters use Biowheels). Some media types can perform 2 filtration functions (Aquaclear sponges mechanically and biologically filter).

Media examples by filter type:

Fluval - BioMax. Or you can go to Pet Warehouse and look at some biomedia alternatives.
Magnum 350 Deluxe - you'll have to use with a UGF; otherwise no biofiltration.
Magnum 350 Pro - Biowheel Pro 60 comes with. You can put biomedia in the media basket for more power, but the media basket wasn’t meant for that.
Aquaclear - sponge. Comes with 1; add a second on top of that.
Eheim Ehfisubstrat, a sintered glass product, or Ehfilav, porous volcanic rock. You could try substituting BioMax or something and see what mileage you get.
Wet/Dry - plastic Bioballs.

Activated carbon - fairly expensive and a luxury. You don't need it but may want it. Basically, some organic compounds stick to it; that's called Adsorption (not ab, ad...there's a difference). It can remove some medications from the tank when you're done treating, may cut down on odors, and some think it makes the water more 'sparkling' looking. It doesn't have the surface area for bacteria of BioMax, but some bacteria grow on it. Needs to be changed at least monthly, or it's just inefficient biomedia. Marineland is a reputable brand.
Ammolock, Nitrasorb, etc...- Dubious value. They bind up ammonia, which is great in the here and now, but since that ammonia doesn't get to your biomedia these can (in theory) interfere with normal cycling! Sooner or later you may not keep up with media changes, and they do exhaust their binding capacity.


When you just want it to look clean (Mom's visiting, etc...). Filter floss is popular. Magnum 350 canisters include a micron cartridge that 'polishes' the water. Mechanical filtration is important in any filter to stop particulate crud before it gums up the surface area in your biological media. In the Aquaclear, the sponge does double duty - biological and mechanical.

Specialty - using peat to lower pH and hardness, phosphate removers, etc...don't worry about this right now. And maybe not ever.

IV.) Overview of Popular Filter Models & Strategies.

Which filter is best is hotly debated and a book in it's own right. There are too many brands & models to review all of them. Based on my knowledge & the market as of 1-13-05, here's my take on the summaries I've read of the most popular brands for turtles:

a.) Marineland ‘Canister’ Filters - Magnum 350 Deluxe & 350 Pro (don’t get the most basic system) & Magnum H.O.T. & H.O.T. Pro: Only the Pro versions have biowheels (2). Biowheels splash too much, unless you have a nearly full tank or provide something for the water to run down. Only get a Magnum 350 Deluxe if you're going to hook it to an UGF, since with no biowheel there’s no biological filtration. That arrangement works well. The output is designed to spray across the upper water in a filled tank, so you’ll need to stop the spray/water fall effect in partially filled tank (a piece of plastic tubing jammed over the output may work fine). Get the Deluxe or Pro; the basic version of the 350 now includes the media basket but lacks the
Double Quick-Disconnect Valves. The H.O.T. is similar to the 350 Deluxe, and the H.O.T. Pro to the 350 Pro (but only one biowheel); the H.O.T.s have a lower flow rate, are less powerful, somewhat cheaper & are canister filters that hang on back of the tank. H.O.T.s don’t seem to lose their prime easily, but wouldn’t be ideal for tanks with a lot of height above the water. Note: The biowheels on the 350 Pro, H.O.T. Pro & Emperor 400 are not interchangeable! You can put biomedia in the media basket for some biofiltration, but it doesn’t hold a lot.

b.) Power Filters – The stereotypical ‘hang on back of the tank’ aquarium filter. Tend to offer great power very cheaply, but if the tank's not full and the power goes out, it could lose its siphon and burn up when the power comes back on. Not recommended in partially filled tanks. Most power filters output water in some sort of water fall of splash that’s annoying in partially filled tanks. Hagan’s Aquaclear is the leading example, and the Aquaclear 500's are cool, if you silicone a sheet of plexiglass to the hood lip to stop the water fall effect. I don’t find turtles in noisy water in nature, and I don’t like waterfalls in my tanks. One of the 500’s key competitors is Marineland’s Emperor 400 - Pretty good in full tanks, but has a pair of biowheels and we've already been over the splash thing. You CAN add additional biological filtration capacity by using Cell-Pore Biocartridges (on clearance so act fast!). In my experience, the Emperor 400 is much less effective than the Aquaclear 500 at coping with low water levels (flow rate drops a lot when the water level is quite low). I only recommend the 400 for tanks that are almost full.

c.) Internal Filters - Some love Fluval 4 internal filters; often I see posts about using 2. I get the impression they aren't as powerful as the external 404 canisters, hold less media and take up tank space. I pass, but some like these. The Duetto 50 & 100 are often hawked for turtle tanks, but widely regarded as inadequate for the purpose. Cute, but I recommend you avoid Duettos, except in small, shallow-water setups like 20 gallon long tanks with under 4” water with young mud turtles). More recently the Whisper line of upright internal canisters (10i, 20i & 30i) for tanks with 2” water & up have become popular, although they produce a water fall like a power filter (this can be dealth with creatively).

d.) Low-End Canister Filters – represented by the ZooMed 501 Turtle Canister & the Fluval 104 & 204 and FilStar XP1 & XP2. On the Turtle Forum, the 501 has gained considerable attention while the others mentioned aren’t posted about often. The 501 is made to sit at tank level; the motor allegedly isn’t powerful enough to merit keeping it under the tank (say, in a cabinet like larger external canister filters). Here’s a nice 501 review Mahler found at Aquarium Life Support Systems. It has a sponge for mechanical filtration, porous ceramic ‘noodles’ for biofiltration & a chamber for activated carbon (which you can replace with more biomedia if desired). Output is via a spray bar. It can allegedly run dry for 30 days (I don’t recommend testing that out…). Another forum member, Charles, reported the 501 can handle fairly shallow water tanks (at least down to 4-5” if the tank wall’s not too tall; Charles said the intake reaches the bottom of a 12” tank), primes easily & doesn’t require re-priming after a blackout. Rated for tanks up to 30 gallons. However, we’ve had enough members post about reliability problems over time that I don’t personally recommend this filter (caveat: I’ve never owned one).

Mid-Range Canister Filters – A tall canister sits below the tank; it’s hollow & can hold a lot of media, & being below the tank won’t lose its prime during blackouts. Hagan’s Fluval 404 - quite popular with turtle keepers. Available for ~$115. Advertised as rated for up to 100 gallon tanks. Includes all needed media. Some fish forum regulars think it's likely cheaper made, less reliable and won't last as long as Eheim canister filters like the Pro II series. If you get a 404, some recommend you fill the canister with water after servicing; I don't think the manual tells you that, and you may need to know. The 404 has a reputation for difficult priming (getting the flow of water started so it can work) in partially-filled tanks; some people hate it, and some aren’t affected. The output is designed to agitate the water surface, so in partially filled tanks you’ll need to put tubing or hose over the output & redirect it below the water. The 404 is a decent choice, but the Rena FilStar XP3 is very similar, reputedly less prone to priming difficulties and advertised as rated for 175 gallon tanks. On the other hand, XP3’s are often a little more expensive and last I checked the XP3 didn’t sell with all the media you need; you need to buy biological filtration (the most important kind) separately. The XP3 has more than one out-flow arrangement option. In one, the XP3’s output tube runs vertically down the inside tank wall & has little holes (a spray bar). In partially filled tanks this can be a problem. You can cut off the output partway down & jam a piece of tubing over it, to redirect the flow under your water. You could cut the output tube above the holes & put a piece of tubing between the upper part & spray bar, retaining the spray bar (yet you can custom-position it thanks to the long flexing tubing). Bottom line: be ready to customize. Note: if the output on the 404 or XP3 is too strong for your smaller tanks, rubber-band a piece of fiber pad around the outflow to cut the current.

Expensive Canister Filters - Eheim Pro II filters - you can even get'em with built-in heaters (like the Pro II 2128)! Eheim filter media is good, but expensive. Well-made filters that last years and years. The Pro II 2028 primes more easily than the Fluval 404 & the output uses a ‘spray bar’ on the end of tubing you cut to fit, so it’s much easier to simply run the output below the water surface & avoid splashing (it’s also rated for a 156 gallon tank). The white fiber pad in the Pro II 2028 is prone to ‘crud up’ & need replacing pretty often (so if you buy a 2028 or 2128 buy extra media packs with white fiber pads). I've seen great things posted by turtle owners; at least one person did think they got clogged a bit easier than Fluval's on turtle tanks. I'd look at the Pro II line, instead of those ECCO's that show up in local pet stores. The one I'd get, the Pro II Model 2028, was around $215 online. A good choice, if money's not a factor. Sometimes sold without media, so make certain you buy a ‘package deal;’ filter & media. Those with thermofilters do have a sensor that goes in the tank so they are not ‘the answer’ for those whose turtles attack filters. I prefer to keep my filtration & heater functions separate so if one breaks I don’t lose both.

Classic Wet-Dry filters - (Besides biowheels or the Eheim 2229, which also use wet/dry theory) - you'd probably only need one. Unless the tank is to be drilled, you'll have to keep the filter above the tank's water level and buy a pond pump to put in the tank and push water to the filter. Uses about 1-3 gallons of bioballs as filter media. You can see one ($200-$300) here. Or look at Eheim's wet/dry canister and I do hear a few great things about the 2229; I've also heard it generates a 'wave effect' in the tank (one person thought turtles might not like that).

Under Gravel Filter - inadequate for turtles unless hooked to a Magnum 350 Deluxe, power heads or equivalent. Has very rarely been implicated in buildup of anaerobic conditions under the filter plate producing toxins that have killed turtles (more an issue during blackouts because water flow stops). Won't spread water flow evenly over the filter plate so sludge gradually accumulates...plan to break the tank down for cleaning every few years. Some people use reverse flow UGFs that blow crud UP out of the rocks where the power filter can get at it, but that's out of my experience. I prefer to remove the crud from the gravel bed by gravel vacuuming during water changes rather than pre-maturely clogging my filter.

i.) Fluidized bed filters – use sand as a biological filtration medium. The Rainbow Lifegard is an example, & has multiple optional filter modules (covering different filtration basics) you can hook up in a linear sequence. One person posted about great success with one hooked to a Magnum 350 with a Reeve’s turtle tank (read about it here; that tank is actually 48 inches by 18 inches wide by 28 inches high), but I haven’t seen enough posts to comment. For whatever reasons these don’t seem to be widely used by turtle hobbyists.

j.) Pond Filters – Frankly, out of my league. Large Poly-Bead filters come to mind. Pond filters are often sold in modular form; you can buy the media compartment here, the pump there, etc… Some people like complete ‘all in one box’ systems so make sure you know what you’re getting. And that your system won’t require you to do any custom plumbing (PVC pipe, sealants, etc…) Remember that pond filters are often designed for outdoor use so check those noise levels before you buy.

Bottom line: If you've got a Wal-mart attitude, get a FilStar XP3 (& some biomedia!) or a Fluval 404 (and remember you may need to fill the canister with water after servicing to get it to prime). If you're a top-of-the-line man, get an Eheim Pro II 2028 or wet/dry. 1 XP3 ought to be fine for up to 55 gallons. Only the ammonia and nitrite test kits know for sure. Factor in any fish you plan to keep, as well as snails, crawdads, etc... Put the intake and outflow at opposite ends of the tank, to create a natural water flow that'll carry more waste to the intake.

If you don't want crud building up in a canister, see the pre-filter section.

UGF - Some use'em, but I wouldn't bother. The awful specter of someday breaking down the tank to clean under the plate is just too much.


V.) What is a Wet/Dry Filter?

Normal biological filter media (say, BioMax rings in a Fluval 404 canister) are submerged. Water flows over them and their bacteria break down ammonia to nitrite to nitrate. Cool. But their bacterial activity is somewhat limited by the low oxygen levels present in water. Oxygen is poorly soluble in water.

But there's a LOT of oxygen in air (21%).

So, how can we bring high oxygen to aquatic bacteria?

A wet/dry filter is wet but not dry. It keeps the media doused with a thin film of water, but not prolonged deep submersion. Oxygen diffuses rapidly across the thin layer of water covering the bacteria, who stay wet (and alive) but have more oxygen to use.

In other words, a smaller amount of biomedia can handle a larger waste load faster than it could in a traditional constantly submersed setup (like the Fluval 404 canister). One post I read in a fish forum said a wet/dry can break down ammonia & nitrite up to ~ 70% faster than a normal canister filter, but emphasized that wet/dry filters are more biofiltration focused & less capable otherwise, so the poster didn’t recommend the Eheim wet/dry for turtles (I no longer have the source reference). That said, the Eheim wet/dry was recommended to me by someone working with setups at the Tennessee Public Aquarium in Chattanooga, TN. I doubt the faster ammonia/nitrite breakdown is crucial, although more water quality-sensitive species (like some map turtles) might be an exception. I’m concerned during blackouts the wet/dry media may dry out and kill off the bacteria faster, although that’s speculation and I don’t know if it applies to the Eheim wet/dry canister filter.

One caveat – wet dry filters maximize exposure of tank water to air. This maximizes oxygenation but removes carbon dioxide from the water, which is bad for live plants. If you have or plan a setup with several live plants, this may be a concern.


VI.) Can I get rid of Nitrate without Water Changes?

            Yes, but you won’t want to do this unless your tap water comes out of the sink with nitrates already high (say, due to agricultural contamination). The device to do it is called a Denitrator. Basically, it creates an anaerobic environment in which bacteria break nitrate down into nitrogen gas, which diffuses out of your tank water. It’s thought that on rare occasion it may produce dangerous substances, hydrogen sulfide being mentioned, but I don’t get the impression that’s a frequent problem. These things are mostly used in tanks with such nitrate-sensitive species as anemones in reef tanks. Another way is with live plants. Their benefits are modest but fast growing plants (Anacharis, hornwort) under strong lighting (i.e.: metal halide or power compact fluorescent) may keep nitrate counts lower. In salt water setups deep sand beds are used to create anaerobic conditions to remove nitrate, but I haven’t heard of this being pulled off in fresh water tanks & certainly don’t recommend you try it with turtles.

            If you’d like to see a commercial Denitrator, check out:

            Nitrate Reductor

            Want to make your own? Check these links out.

Denitrator Plans

Denitrator How-To Discussion

            The main problem with Denitrators is that you may get the idea you don’t need to do water changes because your nitrate levels are low. Wrong! There are other harmful dissolved substances we dilute with water changes; nitrate happens to be one you can buy a test kit for at the pet store. Do your water changes anyway!!!


VII.) Water Changes.

            You need to do water changes to dilute harmful substances in the water. The better filters cut down on this, but you’ve still got’ta do those changes. For indoor setups, I recommend at least half the water every 2 - 3 weeks for openers, and you can monitor nitrate levels and go from there. People with larger outdoor setups with lots of live plants are in a different category I’m not ready to discuss here. If your filtration is good enough, you’re doing water changes to dilute nitrate and dissolved solids, as well as to replace trace minerals, NOT to dilute ammonia or nitrite. Perhaps you’ve heard of water ‘hardness,’ which refers to some dissolved minerals in water (in much of the U.S., tap water is moderately to very hard). When tank water evaporates, it leaves behind dissolved solids (like nitrate & minerals causing hardness); if you just top off evaporative losses with tap water (thus adding even more dissolved minerals), over time your tank’s hardness & concentration of nitrate (& other things) will become extreme – this is unlikely to be healthy for the turtle.


VIII.) What Test Kits do I need?

            Ammonia, Nitrite & Nitrate. The chemicals can get old; I’m not sure when to replace a kit, but be aware. After 4-6 weeks your ammonia and nitrite levels should read close to zero; the kit will tell you how much nitrate is acceptable. PH and water hardness kits are also useful, although not directly relevant to filtration.


IX.) Pre-filtering.

            One annoyance with canister filters is the need to periodically disconnect the hoses, unplug it, carry it to the sink, pop the clamps, lift the top and take out the sponges to wash off all the gunk (uneaten food, turds, plant bits, etc…). You can cut down on this by pre-filtering.

            All this involves is putting a sponge attachment on your filter’s intake, so the sponge does most of the mechanical filtration. You can pop off the sponge and wring it out in the sink, or squeeze it a few times while doing water changes and sucking up the crud (harder than it sounds; makes a cloud). Since less crud gets in the canister, you don’t have to clean it so much. And some bacteria colonize the sponge.

            If you don't want crud building up in a canister, for smaller tanks you can get a nice sponge pre-filter at (the FILTER-MAX III) and it'll pre-filter water before the sludge gets into your canister. I’ve tried them on my Magnum 350 Pro, Fluval 404 & AquaClear 500, and I like'em. I’ve also tried rubber-banding large pieces of fiber floss around my larger filter intakes; it does work, but they have to be changed more often than the canister. I believe panty hose has also been suggested…

            In the Eheim Pro II 2028 & FilStar XP3  it may be worthwhile to avoid using the fine particulate filtration pad (Micro-Filtration Pad in the XP3)at the top of the media stack since it can clog quickly in high particulate tanks.


X.) Safety.

            I’ve seen a number of forum posts that read like this: ‘Recently I went to check on the tank, and my little RES was trapped with his head sucked up the filter intake tube because the intake strainer fell off!!! I thought he was dead! Over the next few hours he slowly came around and now he seems to be active and eating. He did have some hemorrhaging of the eyes. He seems okay, but of course we have to wonder if there’s brain damage and what the long-term effects will be.’

            Folks, turtles don’t breathe water and these filters are powerful. Make SURE those filter intake strainers are wedged on tight when you have small turtles. You can use a little silicone or epoxy to ‘glue’ the strainer to the intake tube; they don’t bond as well to plastic as I’d like, but could help.


XI.) Where To Buy.

            There are 2 Online vendors highly regarded by both turtle and fish forum regulars for great selection and low price. Which is the better buy varies.

Big Al’s Online

Pet Warehouse

That Pet Place

            I’ve seen people favor one or the other. I’ve used all 3 & had good results.

And that’s all I’ve got to say as of 1-13-05. I hope it’s been helpful;)!


Richard Lunsford.