May sound like silly questions but, do you have a filter (if so, are you changing the filter cartridge monthly?)? Do you do partial water changes on a regular basis? Do you use a water conditioner to remove the chlorine from the tap water?

As long as you are doing those things I'm not sure what's going on with your water... If you feed more than the turtle eats at once and the food is breaking down, you may want to cut back on the amount you feed and just give several small meals instead.

Good luck,

-Joe-
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0.1.0 Colombian Red-tailed Boa (100% Het. for albino)
0.0.3 Western Hognose Snakes
0.1.0 Plains Garter Snakes
1.0.0 Red-sided Garter Snake
1.2.0 Barred Tiger Salamanders
0.0.1 Red-eared Slider
1.3.0 Mice
50 million Guppies
50 million Crickets
50 million Mealworms/Beetles