ok i am writing this for a friend that just called really panic, since i have a pool and he was house sitting for a house that has one, he was supposed to put a jug of chlorine on monday, but forgot, so he bought a 1 pound bag of shock(Hypochlorite) and put in deep end of pool , when he looked back he said that every spot the shock touched is all stained , a black stain, we are going to try to take it out with acid tomorrow , but i figured maybe someone here would know what to do , and why did it happen, he checked the pool with one of those test strips and every thing was ok
thanks
thanks