All About Turtle Tank Filters

All About Turtle Tank Filters

Turtles produce lots of waste but enjoy clean water, thus requiring a high-quality filter.

We’ve said it before but it bears repeating – don’t skimp on turtle tank filters!

Proper filtration is the foundation of any setup and is normally the weak spot in most peoples’ turtle tanks. This is not the fault of the average consumer, however. If you don’t have prior, extensive experience maintaining turtles or well-stocked aquaria, you really can’t appreciate the level of filtration these animals demand.

As such, many people easily fall for “bargain” models that just don’t suffice. The result: green and/or smelly tank water and most likely a sick and/or unhappy turtle.

Let’s first take a quick look at exactly why you need quality filtration, after which you can review some our “best-value” recommendations that should keep you and your turtle happy for years to come.

I apologize that this post is a bit lengthy. If you want to jump directly to our filter recommendations, click here.

Turtle Tank Filters Must Provide Great “Biofiltration”

There are three types of filtration used for aquaria generally, mechanical, chemical and biofiltration.

1) Mechanical filtration. This simply refers to a filter’s ability to take out relatively large suspended particles or debris – things that are basically floating in the water. This is accomplished by passing water through virtually any type of media that effectively strains the water. Of all the types, this is the most inconsequential type as far as most turtles (or fish) are concerned, since floating debris is easily handled by any filter and is mostly a cosmetic issue more than any other.

Be wary of turtle filters that require constant use of "cartridges."

Carbon cartridges need continual replacement.

2) Chemical filtration. The type achieved by using certain chemically-reactive media that catch and/or neutralize certain water impurities or contaminants (like chlorine, metals, etc.) through a binding process. By far the most common chemical filtration used in nearly all filters to some degree is activated carbon. This usually takes the form of a cartridge containing a black, charcoal-like granular substance. Activated carbon works by “adsorbing” (note: I did not say absorb) or chemically-trapping things like organic molecules, chlorine, some heavy metals, medications and various dyes (including chemical types dyes or natural “tea” staining resulting from tannic acid leached from bogwood, for example). Again, while activated carbon may be useful in some cases, such as helping to clear up wood-stained water or the dye coloration from fish medicines,¬† it is not important to either fish or turtles in the long run and none of my many, many aquaria over the years have relied on it. Moreover, activated carbon becomes exhausted in time, usually in a couple months, after which time it cannot adsorb anything more and must be replaced. This is why filter manufacturers’ love the stuff. Can you say repeat buyers!

3) Biological filtration. This is the only filtration that really matters, especially to your tank’s inhabitants. Why? It’s the only type that can break down a fish or aquatic turtle’s most toxic waste product – ammonia.

Ammonia & The Role of Denitrifying Bacteria

Ammonia must be controlled through effective biofiltration.

3D structure of ammonia.
by Ben Mills [Public domain].

Unlike terrestrial vertebrates, most aquatic vertebrates, including fish and aquatic turtles, produce their liquid (nitrogenous) waste in the form of ammonia. The ammonia they produce is analogous to our urine (which in our case is in the form of urea). Ammonia is energetically less costly to produce than more complex waste products, like urea or uric acid. The reason why most terrestrial vertebrates don’t produce ammonia is because it requires a lot of water to make, which would be very wasteful for land animals that can quickly become dehydrated. Aquatic animals, however, are constantly surrounded by water so ammonia production is the cheapest way to get rid of nitrogenous wastes. Ammonia is also produced through the process of decomposition when organic matter (like dead plants, animals, uneaten food) decays. So what’s so bad about ammonia? For one it is toxic to aquatic life, especially fish that can be killed at very low levels. And second, it just makes your tank smell bad – really bad. Remember this, no matter what your local pet store may tell you – activated carbon does nothing to neutralize ammonia.

The only thing in any filter than can detoxify ammonia is bacteria, denitrifying bacteria to be exact. These microscopic organisms actually feed on ammonia and through the process of oxidation, break down ammonia to nitrate and then nitrate, which are comparatively harmless molecules to aquatic life. Over time, these bacteria naturally colonize just about all surfaces in the aquarium, the substrate, walls, decorations and especially the filter media¬† – where there is a steady supply of oxygenated water. Unfortunately, these bacteria are not immediately present in a new tank, which is effectively sterile. It usually takes 4-6 weeks at minimum for sufficient levels of these bacteria to take hold before fish can be safely introduced to a tank. This is precisely why fish in most new tanks perish. It is the lack of sufficient denitrifying bacteria that is the cause of this condition, known as “new tank syndrome.”

Turtles are not nearly as sensitive to ammonia as fish, but ammonia can irritate eyes and mucous membranes at low levels and cause greater harm at higher concentrations. Moreover, since they necessarily drink the water they swim in, ignoring proper filtration forces them to drink their own waste. And turtles produce much more ammonia than fish given their much larger size, big appetites, and very messy eating habits. As such, you need much more denitrifying bacteria in a turtle tank compared to similarly-sized fish tank.

Turtle Tank Filters Must Support a Lot of Denitrifying Bacteria

Internal filters are rarely sufficient for larger turtles and tanks.

Internal filters support little denitrifying bacteria.

As I stated, this bacteria can and will colonize any surface in the tank, provided it receives good water flow over it (these bacteria need a steady stream of oxygenated water to work best); however, there is just so much surface in any tank, and the bacteria will not simply pile up on each other. A filter that uses virtually any type of media packs a tremendous amount of surface area for bacteria in a relatively small space and is the most efficient way at housing these friendly microbes. That’s the entire concept behind a simple sponge filter, for example. The sponge matrix does provide mechanical filtration, but it’s really just providing a scaffolding on which denitrifying bacteria grow; and the air pump merely creates a flow of water through the sponge that delivers food (the ammonia) and oxygen they need.

While a sponge filter is great for fish tanks with a light bio-load, and I highly recommend them, they just cannot house enough bacteria to handle the massive amounts of waste produced by anything larger than hatchling or very small turtles. The same goes for most internal “turtle” filters, which in many cases are even less effective than a sponge filter. Likewise, the ever-popular hang-on-back filters are also lacking when it comes to turtle tanks, and usually have only a small area dedicated to media. Unquestionably, the best type of biofilters are the ones designed to fit lots and lots of media – we’re talking about canister filters.

Why Canister Filters Make The Best Turtle Tank Filters

Canister filters make the best turtle tank filters - there's no debate!Yes, canister filters represent a greater up-front cost than most other types, but it’s well worth it when you consider the superior filtration they deliver. In addition, the media used for these filters can be very simple, and include DIY materials. Although the traditional ceramic media works well, so do things like plastic pot scrubbers, small plastic hair-curlers, lava rock, coarse gravel, and chopped up upholstery foam. Whatever is inert, provides a surface for bacteria, and still allows water to freely pass through it can work. For example, for a typical 3 or 4-tray canister filter, I will generally use a course media on the bottom tray (where the tank water first passes), like lava rock (or commercial ceramic media), then move to finer pore-space media as I go upward like gravel, then plastic pot scrubbers, then topping off with a thin layer of filter fiber to polish the water.

Our Picks For Best Turtle Tank Filters

Below are what I’d consider very good canister filters. Each is listed with their recommended capacity. You will note that I have not included most so-called “turtle filters” here. Technically, there really is no such thing as a “turtle” filter anyhow, just filters of varying quality and performance. Forget about the marketing material and just get the best canister filter you can afford; you and your turtle will be happy that you did.

Model & PriceRecommended Tank SizeAvg. User Rating
5 -10 gallons4.2 / 5.0
10 - 20 gallons4.1 / 5.0
10 - 25 gallons4.6 / 5.0
30 - 60 gallons4.3 / 5.0
30 - 60 gallons4.3 / 5.0
50 -100 gallons4.3 / 5.0
75 -150 gallons4.3 / 5.0
75 -150 gallons4.3 / 5.0
75 -150 gallons4.3 / 5.0
200 - 400 gallons4.6 / 5.0

Maintaining Your Turtle Filter

Please do not make the rookie mistake of taking your filter and periodically sterilizing it, either by passing it through hot water of by using soap. By doing so you effectively annihilate the denitrifying bacteria that are doing all the work! Remember these bacteria are your friends!

After your filter has matured (normally 4-6 weeks after setting up with your turtle), you can clean out the media and inner compartments every couple months (or as needed if flow drops) by rinsing them briefly under cool tap water, but don’t soak them in tap. Chlorine will kill these bacteria if they are exposed to it for a length of time, although a quick rinse in tap water is not enough to put a serious dent in an otherwise healthy colony.

Featured (top photo) credit:
by delta407 under CC BY-SA 2.0

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  1. enrique marmolejo says:

    At my pet store they told me that the canister filters will not work for my turtle’s pond because the pond is at floor level and in order for the canisters to work, the aquarium/ pond need to be more higher than the canister, is this true? this is why I had never bought one of this.

    • Rick B. says:

      While it may be a bit more difficult to prime (initial filling with water so there no air spaces) a canister filter that is at the same level as your tank, it will still work. I have one running right now that is actually just slightly higher than my tank!

  2. Kim Lovell Dallas says:

    I’m making an outdoor turtle pond from a stock tank. Is there a step by step video that I can watch. I’ve never used a canister before and need to learn how to set it up.



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