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