Hey, thanks for reply.
Done another water test and again nothing to make me think it's the water. The rts is going into a bigger tank later this week a 4ftx2ftx2ft (sorry I don't use gallons) though he is still fairly small. Still no clue as to why my gibbicep has died- though thinking it may be rts related. Colour has come back to all but 1 of the bn.tetras and 1 of the neon tetras, one of which i have noticed has a crooked spine (which I've only seen with harlequins).
The newest fish in the tank are the columbians, is it possible THEY could be stressing the others out?
I unfortuatly don't have another tropical tank to seperate sick fish into, but am treating with aqua.salt.
Thanks again for help