I am also new to this site and apologize for putting in reply here but I can not find a Post New Thread button on my computer. I have been having trouble with a green pool and not getting it cleared since the end of June. We opened the pool like normal in the spring/ early summer and did the usual to get it clear. I was having a lot of trouble getting my alkilinity, ph,chlorine, stablizer levels right but we got it clear. Towards the end of June, we shocked the pool on a Thursday night and all was fine. Then on the following Sunday, the pool was totally green. Couldn't even see bottom in the shallow end. We have a 20 x 40 vinyl lined inground pool. I tried the usual shock, vacuum, and backwash treatment but that didn't work. Tried algaecide and sequestering product called Metal Out and that has not been working. We even drained out pool as far down as possible with a vinyl lined pool and refilled. My ph, alkilinity, chlorine, stablizer etc. levels are now all correct and have been stable for almost a week and we continue to shock, vacuum, and backwash the pool but are not getting clear water yet and this pool owner is getting VERY frustrated. Any other ideas?