I'll try to get to the point, but.....there is some history to go over.........
My above-ground pool needed to be replaced last summer because my other one got crushed in the really bad winter of the previous winter
The pool store I have used for years put the new pool up......they had been telling me the previous year that I needed to replace my sand, so......when they installed the new pool, I asked that they replace the sand in my Hayward filter. During the initial installation, they "forgot" to replace the sand.......when I pointed that out, they said they would. While I was not home, they say they came back to the house and replaced the sand.
Then.....for the entire summer of 2015 I had mustard algae that would not go away......following their instructions, I shocked and treated with algae chemistry......spending a small fortune and never getting rid of it. I was told that the town added phosphates to the water, which they seemed to claim might be part of my problem. When coming to this site, I immediately noticed that phosphates are NOT a problem, despite what pool stores tell us, which has now made me even more suspicious.
I bought new sand to replace whatever is in my filter, but thought the winter may have killed any algae, so decided to give everything a try, once again.
The problem is now as bad as last year, despite treating the water again.
So.....my questions are, can algae stay permanently embedded in sand and just keep getting put back in the water?? I can't think of any other reason it would keep coming back. And.....can Diatomaceous Earth be used in a "regular" sand filter?? It seems that it can, but I just want to make sure.
Thanks in advance for any help anyone can give me..............I certainly need it!!!