sounds like water condition/ params to me, it took me two try with caps just because of my water quality but the seocnd try is doing fine under my PC's. I think you have enough lights for the acan, but it would have to be in the upper half of the tank. You can also feed it, to help supplement nutrition, i feed mine mysis sometimes when I feed my suncoral. Id say get a cheap acan from a local reefer and see how it does and go from there.