Here is an article I wrote for another posting but it should help you as well.
Are you sure your fish have Ich or do they have Brooklynella? To tell them apart you have to take a tissue sample and examine it under a microscope. The treatment of choice for Ich is copper but copper will not cure Brook. For Brook you have to use 37% Formalin. Formalin will also cure Ich. So if you are treating for Ich and your fish are not getting better they may have Brook. To treat with Formalin you give your fish Formalin baths. Where you put 1 cc of 37% Formalin (Formaldehyde) in 1 gal of water and dip your fish for a minimum of 45 minutes up to 60 minutes. You do this five times once every other day after 5 dips your fish are rid of Ich and Brook. I also put Formalin in the QT tank. I put 1 cc to 10 gals of water every day during the period I give the baths. Formaldehyde evaporates out of the water within two hours and is not accumulative. It does deplete the oxygen in the water so you need vigorous aeration with air stones in the bath water. Do not use Formalin on fish that have open wounds, it will kill them. After 10 days of Formalin dips, once every other day they are cured of Brook and Ich. The tank the fish came out of has to be fallow, fishless, for at least 8 weeks. The eggs of Ich are in the bottom of your tank and can lay dormant for up to 8 weeks. When they hatch they have to find a host within hours or they will die. Brook's parasite divides and the new cell becomes a free swimmer looking for a host. The swimmer can persist up to four weeks without finding a host before it dies. So a eight week fishless tank can say it is free of Ich and Brook. IF ONE FISH IN YOUR TANK HAS A PARASITE ALL HAVE THE PARASITE EVEN IF THEY SHOW NO SYMPTOMS AND MUST BE TREATED. Don't go through this in the future, QT all new arrives for at least 4 weeks. One more thing, Formalin has a short shelf life so use fresh product and ONLY use 37% Formalin, 15% will do you no good.
