water changes never hurt any thing in your tank if done right with ro and predisolved salt for at least 24 hours it will benefit your system if anything try it and also check you calcium level and alkakinity
you might want to check your calcium level if they are staying out that long (8 days) or feed them for they must be hungry usaully mine come out ever couple days like that and after feeding they retract for couple days
ro removes ab out 99% of everything a 3 ,4 ,5 stage ro unit will allow you tell how free of everything is. ask your lfs what unit he uses but even if it is a 3 chlorine should not be present . later dave :) :)