You said you were using Cu. In your filtration system, do you have carbon? If you do, the carbon will suck the Cu out of the water and you treatment period would prove to be useless. If you use medication, you can't have any form of carbon running in the water. Try a hypo treatment, but be aware of the PH. I ended up killing my 2 YT damselfish and clown. Also, you don't want to treat ich, if that what it is, in the show tank because the parasite goes through a life cycle. In one part of that life cycle, the parasite is a free swimming organism which can and will attatch other fish. It can also live in the sand. The only way to get rid of it, is to have no host in the tank for 30 days. With no host, the parasite's life cycle will stop and die.