Filtration basics for turtle tanks

Note: This article covers the basics. What happens in a filtration system is

a lot more complex. You can get more thorough information from technical

aquarium books. Follow the link for an excellent article on aquarium filtration.

So, you know that your turtles need a varied diet, vitamin D3, and clean water.

One obvious way to keep the water clean is by changing it very, very frequently,

sometimes daily for small tanks. For most people, even for those that like to

splash with water, this quickly turns into a chore that they would like to ban

from their life.

To reduce water changes, you can put your turtle into a huge tank, net debris

every day, or feed the turtle in a separate container. All this will help, but

is either expensive or doesn't actually reduce the amount of time you spend cleaning

turtle poop as opposed to taking your turtle for a walk on the lawn.

To really make an impact on how often you need to pull out the hoses and buckets,

consider installing a filtration system for your water turtle tank.

This article tells you about filtration for turtle tanks based on my own experiences.

I will mention names of products; however, these are by no means the only products

that can meet your needs; they are just products that I have used with good results.

How Filters Work

Without getting into the gory details, filters clean water in two ways: Mechanical

filtration sucks in and traps debris. Biological filtration breaks down harmful

organic components into harmless ones. Bacteria that live in the filter medium do this

wonderful work. If you want to learn more about this, a good book about aquarium

maintenance will give you all the details.

Note that medications and water additives are not removed by biological filtration.

There are a number of products available that remove chlorin (if you wish to do that),

ammonia (better change the water and use a big enough filtration system), and heavy

metals (change the water often enough instead).

Testing the Waters

One aspect of water maintenance in your turtle tank is to know what the water quality is.

I recommend that you purchase and aquarium test kit for that purpose and use it

frequently until you understand the water in your turtle tank and how it changes

over time. The most important measurements for turtle tanks are the pH value and

the ammonia values. You want to keep the pH close to neutral, though turtles are

much more tolerant of a varying pH than fish. Moreover, you want to keep the ammonia

out of your water. A filter helps with both of these. Finding out how quickly the

pH deteriorates and how fast ammonia accumulates, will give you a measure for

deciding how often you must change the water and will help you decide what size

of filter to get.

Some Types of Filters

Small Foam and corner filters: These filters usually run on an external pump, and

they are small. They are designed for small fishtanks and most of them are too small

to be efficient cleaners for turtle tanks. Some of them are open; that is, the foam

is placed on a water intake without a housing. Because a major waste in turtle tanks

are larger particles, when you take out the filter for cleaning, most of the debris

floats right back into the tank.

Biowheels, Waterfalls: These can be used as additional filters, but by themselves,

they don't have enough cleaning power. Also, biowheels without a foam prefilter will

quickly clog and become unusable.

Undergravel Filters: Undergravel filters are great for small fishtanks. For my kind of

turtle tank, I don't find them suitable. They require a lot of small gravel to function

well, since the gravel is actually the filter medium. To clean them, on has to suction

off debris from under the filter periodically. I don't use small gravel in my turtle

tanks, because many turtles will ingest the gravel. I also found that I had to clean

under the gravel way too frequently. Since the turtles will dig into the gravel, debris

and bad chemicals (nitrates, nitrites, and ammonia) get released and poison the water.

Larger Submersible Filters: I find that these work best for medium-sized tanks with

a "reasonable" population densitiy. When I started, the only submersible filter

large enough for a turtle tank was the Fluval, so that's what I am using. The filter

comes in one piece and creates a good suction/current in the tank. The foam cartridges

have enough capacity to handle debris. With the adjustable outlet, one can either

agitate the surface or keep the water near the bottom moving for good motion of debris

towards the filter. The disadvantage of these filters is that when they are removed

from the tank, some of the debris flows back into the water. So, I usually clean them

when I change the water to avoid this problem. Submersible filters are reasonably

priced and maintenance is easy.

Canister filters: These are great, because they are big. You can buy a canister

filter, or you can build one of any size you need. Basically, a canister filter

is a bucket with filter media plus a pump that will move the water through the

bucket. Simple, efficient - and a pain to clean. I've never had a canister filter

that I could clean without swearing. Unless you build your own, they are a quite

expensive; and they do take up extra space. However, if you have a large or heavily

populated turtle tank, this is the way to go.

Note: If you do use gravel or sand in your tank, you will have to vacuum it every

time you change the water, no matter what type of filtration you are using.

* (Marvellouse Idea Contributed by The Nevilles)

I was reading your page on water turtle setups and wanted to add that I have

30 gallon "turtle tank" from all glass aquariums that has one end cut to 1/2 height

and fits a power filter without having the water all the way to the top of the tank.

Filter Media

Foam: Cheap, efficient, and easy to clean or throw away. My choice of medium for

turtle tanks.

Activated carbon: Activated carbon is a water purifier. It does make your

water crystal clear. For turtle tanks it really isn't necessary, because you have

to change the water anyway. In addition, impure activated carbon can release chemicals

that will kill your plants, and I don't honestly know how the turtles will feel about that.

(Activated carbon comes from a variety of manufacturers in a variety of qualities.)

If you are growing plants, activated carbon can also make the water too pure!

It's also expensive, especially if you buy cartridges, and a pain to handle if you buy it bulk.

I've used activated carbon in turtle tanks and found that the benefits didn't outweigh the price.

If you need it, most likely your tank is either too densly populated, or you are not changing the water often enough.

Ammonia removers: These are again used primarily for heavily populated, large fishtanks.

They come as a liquid or as granules. The liquid is added to the water periodically,

the granules make up one layer in a canister filter. For turtle tanks, if your water

tests positive for ammonia, you must completely change the water anyway; there is

usually more bad stuff in the water by that time than just the ammonia. However,

ammonia removers can be useful, for example if you go on vacation and don't want your

sitter to change the water.

Of course, all of these can be used in combination, which is what is usually done

in canister filters.

Flow Rate

Get the biggest filter and the biggest flow rate that you can fit into your tank.

You need at least twice, but better four times of what is recommended for a fishtank

of the same size.


A filter casing plus pump will last for many years. I have one filter that I've

had for ten years. Whatever you spend, if you are happy with your setup, it's

worth the expense. Depending on the size and type of filter you buy, expect to

spend initially between 40 and 150 dollars. You can get excellent deals at stores

during sales, or you can try mail ordering for a price break. (But, please,

don't go to a store, get all the information and consultation, and then mail order.

That's not fair.)

If you use foam cartridges, which only need to be replaced every few months

when they get hopelessly clogged, you are looking at less than twenty dollars

a year for maintenance.

Filter pumps run on electricity, and they don't use much.

Taking Care of Your Filter

All filters need to be cleaned regularly. The bigger the filter, the less often

you will have to clean it. I clean my turtle filters by rinsing them with cool

water whenever I change the water. You should not let your filter clog up

completely as clogging will keep water from flowing over the media which means the

beneficial bacteria don't get oxygen, which means they'll die, which means your

filter won't work and in the worst case will release toxins into the water.

Note: Do not replace filter media at the same time as doing a water change. Also,

since filters get populated with beneficial bacteria over time, it's better to

keep it from clogging through regular cleaning. Every time to replace the media,

you're jumpstarting your filter from scratch, which takes several weeks.

A filter is a living being, and you will have to find out its quirks and habits.

Conclusion or: "So what's in it for me and my turtles"

Instead of twice a week, I change the water in my indoor tank every 2-3 weeks.

More often in summer, when I feed more, less in winter. I feed in the tank and

let veggies swim around at all times.

My very small outdoor pond, which also houses a dozen goldfish, gets changed

every 3 weeks in summer. In winter, when I only feed about once a week, its more

like every 4-6 weeks. Because the filter can get clogged with algae, I clean it

every 3-7 days in summer (depending on the age of the cartridge. New foam cartridges

have a higher capacity for debris, but aged cartridges have a better population of


The water is clear and smells good at all times, and I haven't seen any

shell rot or skin diseases.

Reader Comment on Carbon vs. Foam (Jennifer Moore [])

In order for these bacteria to do their job, they require a steady supply of

oxygen, provided by the water flowing over them. When the filter material

they live on (which can be ANYTHING, including carbon, gravel, foam, etc)

becomes clogged, their oxygen supply is reduced or even shut off. This kills

the 'good' bacteria, resulting in accumulation of those nasty organic


Also, the visible debris (feces, food particles, even fragments of wood or

live plant) is one of the two major sources of harmful organic substances in

the tank. As it breaks down (rots), it converts to ammonia (harmful), then

to nitrite (also harmful), then to nitrate (harmful only in extremely high

concentrations--prevented by water changes). As long as this debris is

trapped on the filter media, it is STILL breaking down and producing toxic

ammonia & nitrite, which is flowing right back into the tank.

For maximum filtration and cleanliness, the filter media that catch the

visible debris need to be rinsed regularly--in a fish tank, this might be

only once every two weeks, but in a turtle tank it should be AT LEAST once a

week and can be as often as every other day. Remember, by the time the media

is even partly clogged, you've lost a substantial fraction of its filtering

capacity, while the 'bad stuff' is still poisoning the water just as if it

were sitting on the bottom of the tank.

The media should also be replaced ONLY when debris remnants are so imbedded

it can't be rinsed completely clean, since you throw away the majority of

your active bacteria when you do, and it shouldn't be replaced at the same

time as the tank and its furnishings are 'cleaned' (scrubbed, dried out,

etc), as that is where the rest of the 'good guy' bacteria reside. The

bacteria living on other surfaces can take up a little of the filtration

slack until the new media is colonized.

As for carbon vs foam, they do different things. They CAN be used

separately, but then you will be getting one kind of filtration and not the

other. Foam does MECHANICAL filtration (trapping solid debris so it can be

removed from the closed system) and providing a lot of surface area in a

small space to maximize the number of filtering bacteria that can live there

and break down the ammonia & nitrite in the water flowing through.

Carbon filtration is what actually neutralizes 'chemicals'--it can remove

from the water many of the poisons found in trace amounts in tap water (we

all know how sensitive our reps are to poisons!), as well as help out with

the ammonia. Since many of the chemicals it binds affect pH, it can also

help stabilize pH. Whenever tap water (instead of name-brand bottled water)

is used in an aquatic system, I strongly recommend using both mechanical

filter media (like foam) and carbon. Carbon should be changed about once a

month in an average system. It can also be 'recharged' by soaking overnight

in the strongest (non-iodized) saltwater mix you can make, but it only comes

back to about 50% effectiveness, so I prefer to just change it.

Incidentally, the helpful bacteria will colonize the carbon as well, so I

generally recommend changing the foam and the carbon different weeks, to

minimize the system's 'down-time' from bacteria loss.

Last, I'm not sure where you heard that activated carbon releases ANYTHING

into the water that could harm plants. It does bind some of the nitrates

(from the ammonia>>nitrite>>nitrate cycle), which plants use for food, so a

system with REALLY good carbon filtration could conceivably STARVE the

plants, but live plants aren't likely to survive in your average water

turtle setup, nor is the average setup likely to have that level of carbon

filtration going, so I'm not sure that this is applicable concern.

The 'activated' in activated carbon means it has been heat-treated to make

the original 'charcoal' (reference the above paragraph: the distinction

between 'carbon' and 'charcoal') release any chemicals it might already be

bound to. This gives the carbon the capacity to bind to more harmful

chemicals before being used up. Activated carbon is essentially a single,

purified element (carbon)--there is nothing there to release into the water,

hence the long-standing, and still valid, recommendation to use it as one of

the layers in setting up frog (talk about sensitive...) and/or plant