My dad's AG pool has me scratching my head. 24' round by 4.5' deep, 15,200 gal. Hayward 1hp pump and older pentair 50 gpm DE bump filter.
We opened it late and there was a good bit of algae on the floor and walls. Shocked it, he didn't want to vacuum to waste (on a sand point) so he went through several filter changes, and eventually bought a dolphin robo-kleen which actually does a nice job.
Anyway, pool is clear and water sparkles. He's maintaining an adequate FC level for his CYA and there is no CC. However, every morning, the floor of the pool is dirtied with a fine brownish gray dust. There are lots of trees around, but nothing seems to be pollinating. The ability to hold a FC residual and lack of CCs leads me to doubt its "mustard" algae, especially since it shows back up to the level it does overnight.
I don't know how to calculate the head for AG pumps, but his flow is tremendous. I suspect he's exceeding his filter's max, but don't know for sure. We recently replaced his pressure gauge, and it's been reading fine, but when the flow visibly diminishes (when he was vacuuming), the pressure isn't going up much like it did in the past. So I'm left wondering if possibly he has a tear in his filter grid that is letting sediment through and back into the pool.
I plan to have him turn his pump off overnight (he'd been running non-stop while we got things going) to test the filter. If there is less deposited on the pool the next morning, it would point to a filter problem, right?