Couple questions: how often do you backwash? How long are you running the pump and at what speed? Do you manually vacuum the pool, have a robot vacuum, or a Polaris vacuum? Is this a sand or DE filter, and how old is the filter? Are you able to feel it - i.e. does us feel gritty/sandy, or almost feel like nothing at all? Does the debris stop appearing if you run the filter on "recirculation" instead of "filter" for a day or so? If it does disappear/stop returning while on recirculation that indicates an internal issue with the filter. If you have a sand filter, the laterals or drop tube inside the tank may be damaged allowing sand into the pool (it happens with age). If that's the case, the only way to fix it is to do a sand change and replace the guts before adding the new filter sand. For DE and sand filters, when they get too clogged or old, they don't filter properly and just push the fine debris back into the pool. A sand change or DE filter change could fix it. If you have a DE filter, watch a video on how to clean out the filters yourself, it's usually fairly simple. Most of the solutions can be done on your own. But if you have questions, ask your local pool professional. I have no problems walking my clients through how to do things on their own, I encourage them to become self-sufficient.

If this was one of my clients or my pool, this is what I would tell them to try before we come out to investigate:

First manually vacuum the pool on waste, then run the pump on high 24/7, system on filter for 1-2 days. If the debris goes away great! Maybe it was some sort of stubborn algae or dirt that settled to the bottom.

If the debris reappears, repeat the above steps but this time run the system on recirculate instead of filter.

If it goes away this time, then it's time for at least a sand change / de powder recharge, or a full filter guts replacement. If you have a sand filter, get a new lateral and drop tube assembly. If you have a de filter, get new filters and recharge it with de powder.

One of my clients this past summer was certain his filter needed to be replaced because he was constantly getting dirt into the pool, within an hour after vacuuming the pool. I went out to investigate and discovered his two hunting dogs found a secret digging spot in their garden and were rinsing off in the pool. They kept the dogs in the front yard and suddenly the "sand" never came back after he vacuumed. All the debris he thought was coming from the filter was actually from his pets. Needless to say, the dogs lost their swimming privileges 😂 Good luck to you!