But you need to get the stingray clear of any ich, or otherwise you are wasting your time treating the other fish. Once you put the other fish back in display with the stringray, the stingray is just going to reinfect the other fish. The stingray may never become symptomatic, but the chances of him being infected are very high since he was kept for a while with other fish infected, and he will continually infect all other fish until you get him clear of ich. If cupramine is not an option, then you need to find some alternative otherwise treating your other fish to put them back in the display with the likely infected stingray is a pointless excercise. If you are not going to treat the stingray and are going to keep the other fish in the same system, then it is a waste of time to treat the other fish and would just feed well and keep water quality high.