Ive used it and it had no ill effects on my tank. Whether it was beneficial to helping with ich i am unsure, when it was used the fish seemed to be better sometimes, however i cant say if this was just a coincidence as the fish gained some form of resitance. So using it will not be bad, just whether or not it helps is the real question, at least its something to try to help, but its by no means going to save your tank when things get rough as such. Its quite expensive and the amount of bottles you will probably end up going through, might be better spent om investing in a quarantined procedure imo, which will be able to prevent outbreaks, especially with all the diseases prevailent within the hobby currently.