After years of having a tank my fish showed with ich. I was lucky in the fact that it was a fish only tank so treatment was easy. My source was a heating problem. My tank dropped to 72 and then back up to the 78 and bang, ich followed. I did find some stuff at one of the stores that is reef safe 100% organic that is suppose to treat ich. I don't know how effective it is. I used it one day and the tank became very cloudy. The next day I switched to a copper treatment and a galic regimen. Don't know what your temp is sitting at but make sure that you keep it around 80 also if you don't have anything too tempermental in the tank try the hyposalinity test just not as drastic. The problem not taking them out will be that the ich will continue to drop and spread to the fish. Try removing the one with ich to OT as this is the most important. Also try a fresh water dip.

As for the drop, I found this can happen after a while even if you don't have a load on your tank. I don't know what other people's opinions are about this but I have used sealab no.28 with great success. I drop a tablet in once every two weeks for my 30 gal. It helps prevent ph swings, stablizes my calcium and alk levels and everything seems to like it. It really doesn't add anything to the tank it is just a stabalizer from my understanding and since I have to treat so much for ph levels I needed it. One tablet costs me $2 so it was well worth it.

Good luck and keep us posted.

Angie