tri sulfa is an antibacterial if i remember correctly, though i could be wrong, i've never actually heard of anyone using it for ich before. my advice would be to just go with the standard rid-ick or quick cure, formuline and malachite green. use the doses instructed, i believe 5ml per 10 gallons, and do a 25-50% water change before each dosing. you can treat every day or every other day, but treat a minimum of 14 days, i like to go 21 days to be safe, but i does every other day. if you do this, your fish and tank should suffer no ill affects at all.
usually i deal with small fish and invertebrates though so you may be able to get away with a stronger dose, but i don't really see that it would help anything. ich is not a disease that can be cured quickly no matter what you do. depending on the tank conditions and your particular strain of ich it will take x amount of days regardless of how you treat it.
oh and specifically addressing your question, yes i would say that there is a very real chance that it will harm your bacteria colony. in fact, i would say that there is a better chance of wiping out you filtration then the ich. but then again, i have never seen it in action against ich.
Last edited by cro117; 07-15-2011 at 04:27 AM..