Red-Eared Slider Water Management: Filtration & Treatment

red eared slider filters and water management

Since red-eared sliders spend the majority of their time in water, that water gets dirty very fast. And when you have a tank or pond full of dirty water, it quickly becomes a health hazard to the turtle as well as to you. So how do you keep so much water clean? With frequent water changes and a very powerful filter.

Introduction to Aquarium Filters

Filters are machines that gradually and continuously clean the water in an aquarium or pond. This makes turtle enclosure maintenance much easier because it reduces the need for complete tank cleanouts, saving you a lot of time.

There are 3 types of filtration: mechanical, biological, and chemical.

Mechanical filtration removes the largest pieces of debris from the water, like poo and uneaten food. This requires mechanical filtration media such as sponge, filter floss, or other material that traps particles as the water flows through.

Biological filtration encourages the growth of beneficial, nitrifying bacteria in your turtle’s water. These bacteria turn toxic nitrogen waste into less harmful byproducts. These bacteria grow on the media of a mechanical filter, but it’s generally better practice to use a specialized bio-media such as Seachem Matrix, ceramic rings, because they have a relatively huge surface area for hosting the bacteria, which means more reliable filtering and water quality.

You can’t have beneficial bacteria without adequate water movement (such as provided by a filter). These bacteria need flowing water for beneficial aerobic anaerobic operation. If the water becomes stagnant, they become anaerobic and can make the water unhealthy.

Chemical filtration uses activated carbon to remove some chemical elements from the water. If the water is not filtered, the smaller particles of organic waste obstruct the effectiveness of the charcoal. This is most commonly used for fish tanks, where chemical buildup can happen quickly. Carbon filtration media has a limited service life and needs to be changed periodically to remain effective.

Aquarium air stones are not filters, but they are a useful addition to any aquatic enclosure because they help aerate the water, which nourishes plants and good bacteria, helping keep the water clear. Depending on the size of your enclosure, it may be a good idea to run more than one air stone. Also note that you will need an air pump to make the air stone function.

What are the Best Red-Eared Slider Filters?

For a red-eared slider filter, you need something that offers primarily mechanical and biological filtration, but chemical filtration is not a bad addition.

Canister filters are generally agreed to be best suited to the dirty work of cleaning up after a turtle 24/7. They can hold tons of filter media, which makes them more effective. They also help create a current in your turtle’s water to keep it well oxygenated. Canister filters are expensive, but if you’re going to make a significant investment into any one aspect of your turtle’s enclosure, this is it.

Top-rated filters for a 90 gallon/340 liter (minimum) turtle enclosure:

If you can’t afford to buy a ready-made canister filter, you can DIY one. You can find instructions on how to do so here.

Most aquarium filters are designed with fish in mind, which is a much lighter job. So the general rule for turtle tanks/ponds is that you should buy a filter that is rated for at least 2-3x the amount of water in your enclosure. When in doubt, opt for more rather than less filter power. Some people swear by using two smaller filters rather than one big filter, especially for particularly large turtle tanks.

Either way, you will need to buy filter media. Filter media is the stuff that makes your filter work, and it’s usually sold separately from the filter itself. If you are experienced with aquariums and filters, you can customize the media to your exact needs. If you’re a total newbie, just rely on the manufacturer recommendations for the filter you bought.

PRO TIP — Don’t bother with under-gravel filters, internal filters, or filters made for fish or small tanks. Even hang-on-back filters are unlikely to be suitable for the needs of an adult red-eared slider.

Red-Eared Slider Filter Maintenance

Don’t forget to maintain your filter regularly!

The mechanical aspect of your filter sifts debris out of the water, thereby keeping your water clean, but where does it go after it’s been removed from the water? It stays inside the filter, building up layer by layer. This means you need to occasionally clean your red-eared slider’s filter to remove the debris that’s clogging it up and keep your filter running at peak efficiency.

Set some time aside to clean your filter at least once a month. Make sure your hands are dry and that you’re not standing in water when unplugging or plugging in the filter, as this prevents electrical shock.

  • Disposable mechanical filter media can be thrown away and replaced with new media.
  • Filter sponges can simply be rinsed out in the bathroom sink, but they don’t last forever, so keep some spares on hand to use as replacements when the ones in your filter get too nasty.
  • Lava rock, ceramic rings, beads, bio-balls, and gravel filter media only need to be rinsed until they wear out, at which point they will need to be replaced.
  • If possible, don’t rinse your filter media with tap water. Instead, use water that was drawn from your turtle’s enclosure. This helps preserve the beneficial bacteria population inside your filter and prevents a potential crash.
  • NEVER use soap or chemicals of any kind to clean your filter media!

PRO TIP: To make filter cleaning easier, keep your filter media inside mesh filter media bags.

Cleaning a filter is dirty work. And not all of the bacteria in your filter are friendly or harmless to humans (ex: salmonella).  So here are some hygiene notes to keep in mind during and after filter cleaning:

  • Don’t use your kitchen sink for cleaning your filter — or the kitchen at all, for that matter. Or any space that is near food or used to prepare food.
  • Use rubber dishwashing gloves if you have any open wounds/cuts on your hands/arms. Honestly, this is good practice even if you don’t have any open wounds. And this should go without saying, but DO NOT use the same gloves that you use for washing dishes for filter maintenance.
  • After you’re done, disinfect all surfaces that were used for cleaning the filter. F10SC, Rescue, and Clean Break are popular veterinary-grade disinfectants, and personally my first choice. However you can also use a strong household disinfectant if you prefer. The important thing is to pay attention to the disinfectant’s recommended contact time!
  • After cleaning, scrub your hands and arms with soap and water. Then dry them and liberally apply hand sanitizer.
  • After cleaning, take off the clothes you were wearing and wash them.
  • It’s also a good idea to sterilize your rubber gloves, too. Stick them in an empty dishwasher and run it as hot as it will go. If you don’t have a dishwasher, stick them in some boiling water.

Water Changes

You already have a filter set up, so why do you need to do water changes too?

If you’ve never an aquatic animal before, the most you’ve done in terms of water changes is change the drinking water in your pet’s bowl. The concept here is similar, but since your turtle is drinking and living in this water, changing that water on a regular basis becomes especially important. This is going on all the time in nature — to oversimplify it, think of the water cycle. Water is removed from a body of water via evaporation, it becomes a cloud, which rains down to the earth, and eventually that water makes it back to a pond, lake, or ocean. Not a perfect explanation of everything that’s going on, but you get the idea.

Routine water changes are critical to your turtle’s health because it:

  • Decreases nitrogenous pollutants (ammonia, nitrite, nitrate)
  • Removes waste
  • Improves water clarity
  • Restores trace elements and essential minerals

Filtering alone is not enough!

How often should you change the water?

Red-eared sliders and other pond sliders are quick to get their water dirty, so you’ll need to change the water once every 1-2 weeks. Changing out the water helps keep the amount of nitrates in the water at a manageable level. Ignoring water changes will lead to nitrates and bad bacteria building up to toxic levels in the water, making your turtle sick. 

How much water should be removed and replaced?

You don’t need to replace all of the water in your turtle’s tank. However, you do need to remove and replace ~30% of the water in your tank or pond. For a 90 gallon/340 liter tank, that’s 27 gallons/102 liters of water.

This is still a lot of water to move, so rather than going back and forth with a bucket, it’s more efficient to use a siphon. Many people recommend the Python No Spill Clean and Fill Aquarium Maintenance System because it helps with both emptying and refilling the tank/pond. For obvious hygiene reasons, do not use your mouth to start the siphon.

You can drain the water into a bucket, utility sink, or drain it through a window. Turtle tank water is great for watering plants if you have a flower garden — aside from nourishing your plants, this is also a sustainable way to recycle water. NEVER use turtle water for watering plants intended for eating, and NEVER drain water from a turtle tank into a sink used for eating (ex: kitchen sink). Remember: turtles are frequent carriers of salmonella and this can make you and your family sick! Whatever sink you use, make sure to still disinfect it afterward with bleach, chlorhexidine, or (my personal favorite) F10SC. Make sure to let the cleaning solution sit before wiping it away so it can actually kill the germs.

When you refill the enclosure, if you’re using an aquarium, the water level should be low enough to prevent the turtle from escaping. If you’re using an enclosed pond, the water level should be high enough for the turtle to easily climb out onto land.

Are water treatments safe to use with red-eared sliders?

If you’ve kept fish before, water treatments and water quality is likely a big concern for you. The good news is that pond sliders aren’t as sensitive to the chemical balance of their water as fish are.

However, if you’re concerned about chlorine and/or chloramines in water, use API Tap Water Conditioner or Seachem Prime, dosing according to the instructions on the product label. Only treat the amount of water you are adding to the pond, not the total volume of the tank.

How to deal with algae

If your water starts turning green or you find green stuff spreading on the walls and tank décor, that’s an algae bloom. It’s annoying and unattractive, but fairly harmless. It can be easily removed from décor by scrubbing at it with a sponge or cleaning toothbrush. Magnetic algae scrapers are a convenient way to remove algae from aquarium glass.

Performing regular water changes and using a good filter or two helps keep algae at bay, but if you’re still having trouble with it, adding a bit of API Aquarium Salt can help resolve the problem.


  • Investing in a powerful, high-quality filter is key to your red-eared slider’s health.
  • External canister filters are best for turtle tanks.
  • Purchase a filter that is rated for 2-3x the amount of water in your tank.
  • Regular filter cleaning and maintenance is required to keep it working.
  • Partial water changes are required once every 1-2 weeks on top of good filtration.

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