Bizarre dirt problem in pool

[MattW]

Could it be that the slight bit of dirt is just in suspension while pool/spa is in use and then when all quiets down again, it resettles back to the floor?

That is entirely possible, but what's confusing me is the difference in the amount of dirt that settles based on whether the hot tub was running by itself for an hour or so before switching over to allowing the water to flow into the pool.

To say I'm a little perplexed is an understatement.