We installed a 43’ x 18’ freeform fiberglass pool in 2009. It holds 18,000 gallons of water. We first put on a UV light and used chlorine tablets with it. Ended up taking the UV light out because several pool people said it probably wasn’t helping. Two years ago we had some brown stains on the walls. Treated it with Stain free and it cleared up. Last year the walls were turning brown again. The water was clear and testing good so decided to wait on treating the stains. I shocked the pool in April and got the PH down to 7.2 with a low level of chlorine. Added Stain free and Metal free. Walls turned white. 3 days later the pool is green. Did that same treatment 3 different times because pool would turn green after several days. Sometimes bubbles would cover the surface. After one treatment we added liquid chorine. We have manganese in our well water. Sometimes adding chlorine makes it turn brown. We have a chlorinator that I keep full of chlorine tablets. Our pool store says a number of people are having this same problem. Our last big treatment was Sparkle Conquest, Arenda SC-1000 , and curator. The pool turned blue but was still cloudy. After about 2 weeks it started turning green. I added algaecide that has no metals in it. More bubbles and dark green. The bubbles look like dish washing liquid bubbles.