Don't treat the main tank. It will kill parasites, but it will also kill quite a bit you don't want dead. I'm not at all familiar with Formalin, I know it's very caustic to humans so if you treat wear gloves and a mask. Post on the aggressive and FO forum if you haven't already, there are alot of shark people who know how to treat sharks. I know I don't have an answer for you, but I couldn't let you treat your system. Sorry
