Filtration

This is of utmost criticality. Turtles spend most of their lives in water. In their natural habitats the water gets replaced all the time, but this is not so in the captive habitats. Imagine their plight - swimming, eating, drinking and defecating in the same water!

Turtles generate a large amount of waste - this is because they are messy eaters and also excrete copiously. Turtle excreta comprises both visible solid (and semi-solid) and invisible liquid components. If the tank is not properly maintained (filtered & cleaned) this can cause the water to get filthy, increase ammonia levels and spawn rapid organic growth in the water. The end result - a turtle in dirty water, disease and death!

Water cleanliness can be primarily maintained through two means - regular withdrawal of tank water and replacement with clean water, and a good filtration system.

Water quality is the number one challenge when keeping Red Ear Sliders. Your basic ideal should be to strive for a lot of very clean water. Change the water as often as you can. Imagine you had to swim in and drink the same water. Tab water is fine. If you are concerned about chlorine, let the water sit in the sun for 24 hours before using it. How often do you need to change the water? Well, it depends on the gallons of water per turtle, and whether you are using a filter. I change the water in my 55-gallon aquarium every 14 days, with a strong filter. Keep in mind some foods soil the water more than others. Give your Red Ear Slider as much space as you can possibly afford. In this case, larger is always better. Custom-made glass tanks are affordable. Negotiate the price and features, when you talk to a sales rep. Often extra features like screen tops, which you don't need for turtles, will make things a lot more expensive. Red Ear Sliders and all turtles produce two kinds of waste, visible and invisible. The visible solids can and should be removed with a net, available at pet or aquarium stores, especially larger pieces, before they fall apart. Invisible waste must be dealt with by frequent water changes or filtration. Disintegrating waste produces ammonia. Ammonia is the stuff that is in Ajax, which is bad for people, and it is bad for Sliders as well. It makes them sick, and it can make their skin and shell rot. Every Slider aquarium will have ammonia in it. You cannot avoid it, but you can deal with it. Also note that letting feeder fish and snails swim and defecate in the Sliders tank, will raise the ammonia levels. Also, common dechlorinators also increase ammonia levels. A filter that has settled in or has been running for 4-6 weeks will eventually harbor enough bacteria, like ammonia, and the levels will go down. Filtering over carbon and other specialized filter media also helps. I use a Magnum 350 Pro System with carbon cartridges for my 55-gallon aquarium. If you are using a large canister filter get one about 2 or 3 times as powerful as you would for an aquarium the same size. You will still have to clean and rinse the media more often than for a fish tank. Feeding your Red Ear Sliders outside the tank also reduces waste. Many Sliders will defecate shortly after eating. If you leave them in their feeding tub for a while after feeding, they will defecate, and you get less waste in the tank. Not overfeeding will keep the waste down also. Adding a teaspoon of salt per gallon of water will reduce the level of harmful bacteria and protect the Sliders better from shell and skin diseases. A filter will not only reduce the frequency of water changes, it keeps the muck from floating around and being reingested by the Sliders. So, what filter should you use? One that is as powerful as possible, and one that can filter over mixed media including carbon filter sleeves. Five types of filters can be used effectively with Red Eared Sliders and other water Turtles particularly if they are fed outside of the main tank.There are three types of filters generally available - Underground, Submersible and External.

Filtration System

This is the heart of your tank, so choose well and don't penny-pinch as this could have serious repercussions later on. The filtration required in a turtle tank is twice that of similar size fish tanks. You need to keep you filter running on for atleast 10-14 hour daily. If possible you can time it to run for 2 hrs at a stretch, then stop for 2 hrs…and so on. You should always have the filter running after mealtime.

Canister Filters

The most effective filters for aquariums are large canister filters which fit outside of the tank. They have an outflow tube that carries the water from the tank to and through the filter and an inflow tube that brings the filtered water back into the aquarium. Canister filters are expensive, but when one considers the savings in time and labor as well as the improved appearance of one's aquarium, they are well worth the expense. The filter media will have to be cleaned out and replaced on a regular basis every on to two weeks. Turtle aquariums with these filters can easily be designed to conceal the filter tubing by building basking areas and using some background materials such as rock or bark. Because of the powerful flow created by this type of filters, attractive miniature waterfalls can be designed under the inflow tube. Not to long ago, submersible canister filters have become available in the aquarium trade. This type of filter usually doesn't have any tubes. Instead, the entire canister unit is placed in the water. These filters will work resonably well, but because of their relatively small size they are not nearly as effective as outside canister filters which provide greater filtration surface and rate of flow. In addition, part of the available space in the aquarium will be taken over by the filtering unit. Two advantages of submersible canister filters is that they are relatively inexpensive and their compact size will make them particularly suitable for smaller aquariums with smaller turtles.

When deciding on the pump capacity, consider the amount of water (in liters) your tank contains. Compare that with the flow rate of the pump, which is usually mentioned as X lit/hr. These are ratings obtained under 'ideal' conditions, decrease by 75% to obtain the effective flow rate.

The pump you choose should be able to completely recycle the water in your tank in 1hr, with the 'effective' flow rate. e.g.
Your tank capacity is 200 liters.
The pump you see mentions a flow rate of 400-lit/hr. The effective flow rate is therefore 100-lit/hr. i.e.; this pump can recycle 100 liters of water per hour.
So to completely recycle the water in your tank in 1 hr - you need 2 of these pumps or a single pump with a mentioned capacity of 800-lit/hr.

Internal canister filters

These are relatively cheap and can be highly effective. Use the largest size you can install in your tank. The best filter medium in our experience is of the foam type. This can be taken out and washed whenever it becomes clogged.

External canister filters

For large tank systems this sort of filter is unbeatable. Again, we have found foam media to be the most effective but various other combinations are also possible as one of the benefits of this system is its tremendous versatility. The filter body is located outside of the tank, only the inlet and outlet tubes entering the terrapins environment. Use the largest model you can afford for optimum results - which brings us to the only potential drawback, cost. Good external power filters are not particularly cheap, but definitely worth while if you keep large specimens in an indoor tank system as they will drastically reduce the need for frequent water changes.

Undergravel Filters

Underground pumps are a strict "No-No" for turtle tanks, as they require a fine layer of gravel to work effectively, as it is advisable not to use that in a turtle tank. Most international literature recommends external pumps, and we don't doubt the superior filtration power they have, but feel that a cheaper and equally effective alternative could be 1 or 2 high capacity submersible pumps.

Undergravel filters can work very well, but do require a large surface area, low stocking density, and well oxygenated water. The types powered by an airlift (air pump) are not adequate for anything but the smallest hatchlings. Larger tanks should be fitted with a powerhead in place of the airlift. I like the Aquaclear range.

Undergravel filters run by powerheads can be effective in filtering Turtle aquariums. They work best with large tanks containing few Turtles. When using Undergravel filters, it is also critical that turtles be fed easily decomposed food or in a seperate container because the Undergravel filter will not be able to efficiently filter and break down large food particles. Any such particles will have to be siphoned or netted out of the tank on a regular basis. As an undergravelsubstrate use a 2 inch layer of a small rounded pea gravel. There will come a time when it becomes obvious that the undergravel filter is overloaded. This will mean taking out the Turtles and stirring up the gravel. The resulting dirty water should then be siphoned out. The tank should be filled and the process repeated three or four times. If the enclosure is particularly dirty, then the filter and substrate should be removed, the enclosure thoroughly cleaned and disinfected, the substrate washed out and the entire setup redone. Because, undergravel filters are biological filters that depend on microbial action, it will take up to a week before the microbial flora reaches adequate levels and the filter becomes fully operational.

Sponge Filters

The high quality Tetra sponge filters can be effective with smaller turtles if a high rate of air flow is used. Small inexpensive air pumps are not recommended with sponge filters. Clean the sponge on the filter frequently.

Power Filters

These filters have a limited use when keeping water Turtles because the water level has to be a certain height for the filter to function. This creates a problem when you need space to create a basking area and enough height to contain the animals. Custom-made aquariums with a specially designed opening on the side will allow for the use of power filters. Otherwise, the only option is to have a large tank with the basking areas designed as an island in the middle rising above the top of the tank.

Pool Filters

These can be moderately effective in enclosures with water Turtles. They will tend to get dirty rather quickly and regular cleaning or replacing of the filtering medium will be required.

Here is a more indepth section which has questions and answers for other filtration topics like Carbon and the pH scale.

Carbon

What does filter carbon do? Carbon has the ability to catch certain chemicals that occur in water by adsorbing them. In aquariums, carbon's chief role is to tie up the chemicals that cause discoloration and odors, which are then removed from the system periodically as the carbon is discarded.
Are some carbons better than others? Yes, some filter carbons, the coarse, shiny black stuff, is no more than anthracite coal, and have very limited adsorptive properties. Other carbons are "activated", meaning they were exposed to extreme heat or steam to increase their effectiveness. These dull, lighter, carbons may have hundreds of times the capacity of standard coal.
Should everyone use the highest quality carbon? Many hobbyists use low to medium grades of carbon, but either use it in large quantities or change it often. Others have high-flow filters that can grind the softer, high quality carbons to dust, which is then blown into the aquarium. On the other hand, some filters hold only small amounts of carbon, so better grades should be used.
Do carbons get full? Yes, eventually the filter carbon has bonded all the chemicals that it can handle. How long that takes depends on the quality and quantity of the carbon, and the load of Slider waste. If the aquarium water is taking on an odor or is yellowing, the carbon is full.
Can carbon be re-activated? No. Heating carbon in a household oven might reclaim a tiny fraction of carbon's power, but probably not enough to pay for the fuel to heat it. It is best to discard used carbon.
How often should carbon be changed? Once the carbon is full, it serves very little purpose in the aquarium. Some of the compounds adsorbed by the carbon will eventually break down and be released into the aquarium. Carbon should certainly be changed when colors or odors in the water indicate that it has become exhausted.

Ammonia

How do I keep my Aquarium safe from ammonia poisoning? Normally, Ammonia is consumed by two species of beneficial bacteria, Nitrosomonas and Nitrobacter, referred to as nitrifying bacteria. Nitrosomonas convert ammonia to nitrite to relatively harmless nitrate. These bacteria comprise the biological filter and keep the aquarium free of harmful ammonia and nitrite.
What causes ammonia in aquariums? Feeder fish and Algae eaters continuously release ammonia directly into the pond from their gills, urine and solid waste. Uneaten food, decaying plants and algae also add ammonia to the water.
How do I know if ammonia is in the pond? Ammonia in aquarium water is colorless and odorless. The only way to tell if ammonia is present is by testing the water with an ammonia test kit. The Ammonia Test Kit or Dry-Tabo Master Test Kit enables you to easily test for the presence of ammonia and other important water quality parameters.

PH

pH is the measure of acidity and alkalinity of water. A pH reading of 7.0 is neutral, a pH lower than 7.0 is acidic, and a pH higher than 7.0 is alkaline. The pH should be tested weekly, since foreign material in the aquarium may cause changes in pH and severely stress the Slider. You can pick up the PH test kits at any pet store. They last long and are relatively cheap.

Nitrite: Nitrite is a toxic waste material found in varying concentrations in most aquariums. Nitrite is produced by bacteria in your biological filter as it breaks down ammonia. Regular testing for nitrite is important because high levels of nitrite affect the red blood cells of fish and turtles, and reduce their ability to carry oxygen. This could cause suffocation and death if it is at serious levels.
Nitrate: Nitrate is a waste material found in varying concentrations in most aquariums. It is produced by nitrifying bacteria in the biological filter as it breaks down ammonia and nitrite. As the biological filter grows, the nitrifying bacteria, and Nitrobacteria feed on nitrite, converting it to less harmful nitrate. Nitrate levels should be maintained below 40 ppm. High levels of nitrate may also cause algae to bloom in both fresh and saltwater aquariums.

Water-Changing

The best way to keep the tank water clean is to change it everyday. But that can be quite a tedious and time-consuming activity. Therefore, a most people adopt a partial water-changing schedule along with a filtration system.

The water that you put in the turtle tank doesn't need any special treatment, as long as it is fit for consumption by human beings. Tap water is fine, but its better if you can use water filtered through an AquaGuard or similar device (considering the poor municipal water quality in a lot of Indian cities). If you are not filtering the water, we recommend standing the water overnight in a bucket to remove the chlorine. Chlorine removal tablets that are easily available can also be added, but these increase the water alkalinity and if possible should be avoided.

Some water-changing schedules we suggest (you can follow anyone based on your convenience). These are merely suggestive you can alter the water-changing schedule based on your tank requirements.
OPTION 1: Change 20% of the water every 2 days, replace full tank every 10-12 days
OPTION 2: Change 50% of the water every 5 days, replace full tank every 12-14 days
OPTION 3: Change 50% of the water every 7 days, replace full tank every 17-19 days

(Option 1 is recommended for small tanks, Option 2 is the most convenient for medium to large tanks, Option 3 should be followed only if you have invested in a high quality external filter!)

I recommend cleaning and disinfecting the tank, every time the full tank water is replaced or atleast once every 45 days. You can also add 1 level teaspoon of common salt for every 4-5 liters of water. This prevents the growth of 'bad' bacteria and prevents shell and skin diseases.

Some solutions that help disinfect/keep the water clean are readily available at most pet stores. These can be added as required.

Filter Cleaning

All filters need to be cleaned regularly. The bigger the filter, the less often you will have to clean it, so if you can afford it, go for a bigger filter. Most submersible filters use foam as the filtering medium. We recommend you clean the foam every week, by rinsing it thoroughly under a strong jet of cool clean water. It is also advisable to rinse the filter components/casing.
Filter foam should not be subjected to strong detergents, or other cleaning ingredients, as it tends to absorb these. It could release these chemicals into the tank water later, polluting it.

Monitoring Water Quality

The water-changing schedules and filtration capacity selection process are suggestive - every tank has its unique water purification requirement that is dependent on a multitude of factors.  Eventually (through experience) you will be able to observe the color and smell of water to diagnose when it requires changing. A strong stench or change in watercolor - requires immediate water replacement and a full tank cleaning.

While you spend a few months with your habitat observing water quality and climbing up that experience curve, we recommend you monitor water quality using a simple water-testing kit (for pH level). These are easily obtainable from your local pet store. Use it every 4 days for the first month, changing the water or modifying the filtration equipment to get the desired pH.

A pH level of 7 is neutral, anything more is alkaline and less is acidic. In a turtle tank the desirable pH level is between 5.5 to 7 (i.e., slightly acidic).

Fishes are natural monitors of water quality. And while a fish enthusiast might scrounge at the thought of fishes being used as testers - one cant escape the fact that their increased sensitivity to deterioration in water quality can provide 'visible' early warnings. So you may keep a few fish, and observe their fins, eyes and gills carefully for any changes. (But please don't get too attached to them, as they CAN end up as your turtles' snacks!)