Mech Cb - The only danger the water poses is if the ammonia levels get too high. Since you have a smaller filter, I doubt there is a bacteria cycle going, if there was, then you'd need to worry about the nitrate levels. You can get test strips or just get in the habit of replaced at least 25% of the water probably weekly on your tank size. The bigger concern would be for your fish. Turtles can survive far worse conditions than fish!
mmanchuso - 2 x 4" turtles need at least 80 gallons of water, and you have them in 25. That's way too small, so basically you have too much biowaste for your filter and tank to handle. I'd recommend looking into an upgrade because those turtles will only get larger and you'll need the extra room. For the moment, fill up the tank more, if you can, get it closer to at least 40 gallons, and see if that helps with the cloudiness. However, an actual upgrade will be the best option for you.
