Why would fresh tap water in an above-ground pool turn green while filling the pool?
The above answers are way off – there is no accuracy in either. Your pool may have been on the brink of turning green anyway. The fresh water only excellerated the situation. Your chemical balances were off – both the chlor and pH. Als, in the above 2 they refer to copper stains. And that can only come from a low pH or low Total Alkalinity or both. The stains will appear on the wall and floor surfaces not in the sus[ension in the water. The statement in 2nd that the minerals were corroded is false – you can’t corrode minerals but you can corrode the copper inside the heater by or with a low pH. A solution would be to extend the run time on the filter/pump thru the summer until the weather starts to cool. 6 to 12 hrs is a normal run time for a small pool. So, to finish the rest of the question – extend the filter time to clear the pool, add a boost in chlor by using liquid at 12.5% strength, brush any algae that is clinging to the walls & floor.
