What is it used for and how does it affect the fish. i hear it being used as a treatment quite a lot. if somebody could let me in on the info it would be appreciated, thanks
Personally, I think it's a waste of money except in the very short term for treating some conditions. But the dosage instructions on the packet are useless, and designed to make you spend money IMO. It's more likely to do harm than good to your fish.
I pretty much agree that it is of limited benefit in a freshwater tank. In some cases, it can be dangerous to your fish depending on what you keep. Here is a good thread that will help explains it's uses.