I keep getting debris build up on the bottom of the pool. Here is the scenario - Pool is clean then I run the pump. After a few hours I'll start noticing some debris on the bottom. I'll clean the pool with my robot and/or my manual vac then by the next day more debris on the bottom. Here are a few pics of the debris on the bottom of the pool. Any ideas on what this could be? And what I could do about it?