Hello! This is my first post on this site so hopefully I will give the correct information and background in order to get some help with a potential algae problem I have. I just moved into my house about 4 months ago and the house had a pool that was built in 2008. The pool was in good shape and with just some TLC with cleaning I was able to get it looking great and chemicals balanced. Over the last couple weeks the temperature has drastically increased here in Arizona and I noticed by Acid level was down. I added acid a couple times and its now great and balanced. Unfortunately last week I noticed a black line forming on my pebble tec rolled bond beam. I've attached a picture. Can I get some suggestions on how best to get rid of it? Thank you!