What's wrong with my pool?

We purchased our home 2 years ago. House was vacant for 3 years, pool covered, pump off. We had pool drained & cleaned (muriatic acid wash) before refilling it. New pump & filter. Everything looked good, with the exception of a couple of "worn" spots on the pool floor, until about 4 months ago. Now several areas of the pool look like dirt is ground in to the walls & bottom of pool-some areas worse than others. Filter is cleaned weekly, chemical balance is perfect. We had our lanai floor painted several months before the problem started, & began using a barracuda self cleaner a year before that, but those are the only things that have changed since we opened the pool, and the problem didnt present until months afterward. Any ideas??

Hi, and welcome to the forum!

"chemical balance is perfect" doesn't really give us much to go on. Can you please post your test results on your water, along with what method you're using to test? Do you have any metals in your water? Any problems in the past with sand or black algae?

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