I have a recurring dusting of algae on sides and where the pool vac doesn't reach. It easily brushes off and vacuumed away but comes back in about a week. I've been running chlorine at about 4-5 (free and total) by running my salt generator high but hasn't helped. pH on high side (~7.9) but that's typical -- short of adding acid every week I've never been able to keep it down in this pool. CYA is low since I was trying to push chlorine up. All other levels are normal. Have not tested phosphates in a long time but this pool is screened. But maybe I need to check? Anyone have any ideas?