So in live systems the chlorine will destroy your bbs. You can add chlorinated water to sterile systems without fears of destroying colonies, because they are already destroyed. If he is running live, which I have no idea if he is, he should for sure let it sit out for 24hrs, or whatever that time frame is.
I narrowed the root cause for my rampid pythium growth to me adding clorinated water, then adding hydroguard, it basically killed them as soon as I put them in there. So if hes running high temps, i would not reccommend it, but yea if hes using peroxide and chillers sure why not add it strait to the pot. I think all that sounds correct lol. .im pretty baked