Whenever I run my Hayward Sand Filter I get what looks like dirt in all the little crevices of the bottom of the pool liner. If I clean the pool spotless, it doesn't return till I run the pump again. The water itself is crystal clear, blue. I've acquired the pool with the purchase of the house 5 years ago, and had this problem from the beginning. Not knowing a thing about pools, I mainly thought it was the filter. So, I changed the sand probably 3 times, put in new laterals - thinking they might be cracked, replaced the top lid gasket. Still no luck. I've backwashed, vacuumed to waste, thou not all the time. Now I'm thinking maybe algae. I put a white stocking over the return, I got some white sand, nothing else. But when I did this I hardly got any dirt at the bottom of pool. My pool is 21 feet round. Have a Hayward Sand filter S166t with a 1.5 Speck pump. I've heard the wrong size pump if too strong can cause dirt to return, but all the stores tell me this pump size is fine. I tested the water with the pool store and it comes up great. No issues. One strange thing, I was low on water, after cleaning pool spotless, ran the garden hose for about 2 hours, and noticed some of the dirt was returning to the bottom of the pool.. I was not running the filter!! Then I thought maybe the dirt is coming up from the liner, holes, tears. I found one, 1/2" and patched it. But all the experts tell me dirt will not come up that way, and I would be losing water, which I am not. So back to the filter, garden hose ? Seems like the motion and current is causing dirt ; algae to appear? I'm willing to buy a new filter if that would solve it. The dirt or algae is brown, turns to dust when moved, sometimes leaves a yellowish mark, that eventually goes away. Any ideas, advice , comments, would appreciate!!!