There is a debate about what filter you should be using for turtle tanks. All filters will work but the best filters are canister filters as they are the best for breaking down waste products. Turtle tanks work exactly like a fish tank good bacteria breaking down waste products produced by the tank occupants. Waste products come into the water as ammonia. Ammonia is toxic for tank occupants and good (beneficial) bacteria break the ammonia down into a non toxic form. We then do regular water changes to take away the remaining products. This is just a basic run down on the ammonia/ nitrite /nitrate process.
When we first start a turtle tank we often use a internal filter. As the water level for young and baby turtles is often kept low . You can place a internal filter on it's side to keep it under the water level As your turtle grows you will increase the water level your filter then can be turned up to sit straight. With young turtles or baby's do not use a filter with a large flow rate. When purchasing a filter remember you are not using a full tank of water. Use a size appropriate filter. When your turtle has grown you can use a canister filter which are the best. Theses filters need half a tank of water to run there can be problems using these filters with low water levels.