3 fish dead in 2 weeks and it does not look good for the rest

[kien]

If it appears as tho they are getting a velvetty texture they could have marine velvet. The early stages of preceicable velvet infestation can appear like ich.. Sort of small white spots. If this is the case you may not have any choice but to treat your display tank with copper. Maybe take out most of your live rock and store them in Tupperware while you are treating the fish. If you do use copper whatever live rock and sand you have will have to be thrown out later. A QT tank would be best but you said that's out of the question. If left untreated you will likely lose the rest of the fish, just a matter of time