You need to observe your fish really closely and see if they have tiny white dots on the fins or tail or body of the fish. If you do, the fish have ICH. If you don't see any white dots, well it's still a possibility that the ICH is attacking the gills of the fish where you can't see these tiny white dots.
It can also be ammonia burns irritating your fish, or a really high pH. So you should first check your water parameters and make sure your ammonia is at 0 and the pH level is some where between 6 and 8.
If you do have ICH, you can treat it with raising the temperature in the tank to 86 degrees. Raise it by 2 degrees every few hours until it reaches 86 degrees. Keep it at 86 for two weeks.
If you have ammonia, do a 50% water change asap. Then do 35% water changes daily until ammonia is at 0.