Posted: Fri Dec 28, 2007 2:54 am
Better not to use them at all. The sulfa blocks contain...sulfa which is a medication used to treat a variety of fungal and bacterial conditions. When sulfa is constantly in the habitat the fungus and bacteria living there will develop a tolerance to it. Then down the road if the turtle's immune system is weakened for some reason (injury, too cold, diet, water not clean enough) and he/she gets an infection, then sulfa is useless as a treatment because the infection is resistent.
If the tank is clean, the diet good and the turtle basks appropriately under a good UVB bulb and dries out periodically, then you don't need sulfa.
There's another kind of block that looks very similar which doesn't contain sulfa but only calcium. Putting it in the tank or in your filter won't hurt anything but it isn't terribly effective. A better source of calcium is cuttlebone.
SpotsMama