I have an above ground pool, 10,000 gallons with a vinyl liner and I think I have black algae or something living underneath the liner. The problem started when the pool was opened and it was completely green and dirty. So I figured I would start completely fresh by emptying the pool and scrubbing the bottom with bleach. After filling it back up again and adding all the chemicals, I noticed dark blue stains on the liner. Soon black spots/streams starting coming up and forming around the entire bottom of the pool (First picture). I did a triple shock and scrubbed it for about a week. Throughout the next few weeks I would shock it every few days and the stuff at the bottom would die and I'd vacuum it up. But after the cholrine goes back to the normal level (1-3ppm), the algae starts to form in the same dark stained spots on the liner. I kept the chlorine level high all throughout the next week and continued scrubbing but I am making no progress. Here I am about a month later and it still is coming back. Shocking will temporarily keep it away but it just isn't dying off. Could it be that this algae is underneath the liner itself? It comes back in the exact same spot where the liner has dark blue stains (You can see the stains better in the 2nd picture). No matter how hard I scrub or shock these dark blue spots/streak looking stains remain. Any ideas on what I can do?
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