I do not believe in treatments for fish unless their condition is severe. I have always just fed my fish as much food as they can eat, while maintaining water quality. This always gets rid of ich in my case. If not either its bad water quality, or they are still not eating enough.
Water quality is such a huge subject that it can be hard to pinpoint an exact cause. There are also stabiltiy characteristics that fall into water "quality". If your temperature fluctuates too much it can cause osmotic imbalance, and cause stress , lowering its ablity to fight off disease because it uses more energy to mantain osmorgulation. Also high temperature can cause fish to need more food, because their metabolism needs change to temperature. They are cold blooded so they eat according to the temperature of surrounding water. Then there is pollution variables like ammonia, nitrite, and nitrates.If they are high they will be stressed and be more suceptible to parsitic infection. Especially ich. Also there are things like metals that cause irritation to fish skin, like copper. Some scalless fish are very sensitive to copper treatments, wich can make their condtion worse.
Salinity fluctuations are also a big stressor wich effects the fishes ablility to maintain proper osmorgulation.But thats another story....
I suspect your temp is fluctuating, the salinity is not maintained properly and your feeding your fish not enough. But this is my opinion only.
