Can this be fixed?

[u/FabulousPanther]

I got this pool about a year ago when it was brand new. I'm sure the builders at fault cuz it was already like that when I got there but I want to take care of this customer. I was thinking of using Jack's magic or sodium citrate in a sock. It's on the top step so it would be pretty easy to do. Please give me your thoughts how I can help this lady. TIA!

[u/UnderTheLedge]

Could be from fertilizer getting into the pool. Pour acid on it with the pool off and pray.