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What type of pond do you want, a permanent in-ground pond or something above ground? If you want something above ground, a large stock tank is the way to go. They are designed to hold water and have a drain at the bottom to help with water changes. An in-ground pond requires a little more work and thinking. You have to keep predators out and keep the turtles in. If the turtles are stressed, they'll try to find a way to escape.
To keep predators out, a fence is ideal or just don't give them a way in. Our pond is 2 feet deep and goes straight down, there's no were for a predator to get into the pond. Keeping the turtles in can be a little more tricky. Unless it is a really large pond where the turtles can move from areas that are more stressful for them to other areas that aren't stressful, they will most likely try to escape. Red Eared Sliders generally don't venture out on land except to bask and to lay eggs. When basking, Red Eared Sliders tend to stay at the edge of the pond or ideally on a log that has fallen into the pond so they can quickly slide into the water at the first hint of danger. Red Eared Sliders like to dig, so if you are relying on a fence to keep them in, be sure there is an unground barrier so they can't dig under the fence.
You really need to keep the water in the pond moving and filtered at all times for several reasons. 1) Two adult Red Eared Sliders produce a lot of waste. Even in a large enclosure, the water will turn foul quickly and it won't be healthy for the turtles. 2) Full water changes can be stressful for turtles. You are either pulling them out of their home to change the water or they are watching their home quickly dry up. 3) You will have serious algae problems in a pond that is not kept clean. Algae can very quickly and your tank without filtered water will be an algae paradise. 4) You will have a breeding ground for mosquitos. Mosquitos lay their eggs anywhere there is standing water, even in less than an inch of standing water.
A properly filtered enclosure requires little maintenace. You will probably grow tired of changing the water every week. You will spend a lot of money up front for the filtration (make sure you include a UV sterilizer to keep algae out), but it will pay for itself in saved water and labor.
Good luck with your pond!
Sweeney & Pascal - RES Hatchlings & Martha - 2 yo YBS
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