We have been battling a problem with mustard algae in our pool since last summer. We closed the pool at the end of last summer and hoped that when we opened it this summer we would have a fresh start but that has not been the case. I bought the recommended testing kit and did the test today. We have some chemical balancing to do as our alkalinity and pH are too high and our calcium hardness is too low. We are going to adjust these over the next 24 hours. Our CYA is also lower than the 30 but not 0. The thing that I don’t understand is that we get a reading for combine chlorine of zero (taken both at night and in the morning) and an overnight loss of only 0.2 of free chlorine. We have tried different algicides and they all work for a few days but it always ends up coming back. We were planning to slam the pool but I’m not sure how long we do that for if our overnight pool readings are already showing that we meet the criteria for finishing the slam. If a slam is not needed, how on earth do we get rid of this algae once and for all? I am so confused because I was feeling like a slam with the way to go and was excited to get rid of this algae once and for all but our readings don’t seem to indicate that. Also, we have a vinyl liner pool so want to make sure that we won’t be bleaching our dark blue liner. Please help! Thank you!