I think we're neighbors.

I'm on Baton Rouge Water, use the same pool supply store, and we have the same problem. Sounds like water problems.

In the past, Parish Water (a.k.a. Baton Rouge Water) used local wells purchased from Capital Utilities to augment their water supply when necessary. These wells are notoriously high in iron; I know, because I used to be on one of them before becoming a Parish Water customer.

Anyway, back to your problem. I have the same stains, but I originally thought that it was tanic stains from live oak leaves and such. During Mardi Gras, we went to Colorado for a week. Upon returning, I had a large amount of live oak leaves in my pool. After cleaning it up, the stains appeared. So, I shocked at high levels, which is the prescribed method for getting rid of tanic stains. No luck.

So, I took a water sample to my friendly local pool supply store, but they were closed for the Easter holiday. I happen to have a quart of Metal Out, so I dumped it in. A day later, my stains have faded to the point of barely visable. I plan on another quart or two of Metal Out.

I have not had to top off my pool much, so I didn't think the iron came from the tap water. But, given your and my problem, and the common tap water source, I guess we have too much iron in our tap water and pool.

Good luck.