Yeah the sulfa thing isnt realy a good idea. But adding freshwater aquarium salt (NEVER USE TABLE SALT) to the tank is a great and better way to prevent fungus (what the sulfa block claims to do). I use it with no problem..
But adding freshwater salt alone wont cut it, a good filter and partial water changes is more important and effective.
Since your turtle is a hatchling, he is obviously very fragile and more sensitive to stress and other things (water temp etc) I would keep the water at a good 80 degrees for a little while (for about a month, maybe less) and then slowly drop it down to 78 degrees.
Also make sure that the basking temps are in the upper 80's lower 90's (90 degrees is a good basking temp) and make sure he gets plenty of calcium in his diet. Dont let his ambient air temperature drop as well (the air around him, it should be rather warm (in the high 70's) and keep him away from cold drafts (air conditioner vents, etc.)
You are using reptivite, right? A word of caution, becareful not to overdo it on the supplements because you can overdose him..moist the pellets a little and then sprinkle the powder on (not a lot, not too little) and leave them out to dry overnight, then in the morning, feed it to your turtle.
Just a heads up
