If im doing such a huge water change, a water conditioner(dechlorinator-Wardleys tri-start) is a must yeah? I was worried that chlorine and chloramine in the tap water was harming the bacteria causing ammonia then converting into nitrite then more nitrates? And is it true that treating the replacement water (not the entire tank volume) is useless because you are only targeting that small amount being replaced which will only gets lost in the existing water and doesnt find the chlorine etc