Yes,
you can do hyposalinity in the main tank if you have no inverts.
Since you have a huma-huma my guess is that tank is invert free
I would remove the copper first using carbon for a day or so before I lowered the salinity. Copper and hyposalinity can be used together but it is very tricky and you could kill your fish if you don't have the pH under control.
Of course you may not even have Ich.
That type of scratching COULD be cryptocaryon, but it could also be from gill flukes are amyloodinium. Hypo does not work very well for either of these things.
Try using a flashlight on the fish first thing in the AM. With cryptocaryon this is the best time to see it.
When was your last fish addition?
If it was more than 2 weeks ago chances are it is not amyloodinium either.
This disease kills all fish in the tank very quickly, like the same day you notice symptoms.
If the scratching goes on for a few days and spots are never found and no other fish are affected, you are probably dealing with flukes. These require 3 dips in formalin to cure. If you get to this point check with Ed or Terry and they can tell you what to do.
John
