Fish dying

[jkidd155]

I've been losing fish like hell had 25 n my 265 only have 10 left I've been searching da net n it seem dat I might have marine velvet not 2 sure but i saw my clown have da symptoms so I took him out just n case but got home n my yellow tang dead on the bottom wat 2 do I have corals n fish m my tank wit live rock