Hello, and welcome to the forum!!
Barring an algae bloom, your brown sediment is most likely dirt/pollen/dust that blows into the pool and eventually settles out on the bottom, especially if it keeps settling back into the same places each time. Every pool has a certain amount of this, and there's not much you can do other than to vac it to waste or keep it stirred up in the water so your filter has a chance to get it.
The other two possibilities are 1)iron settling out of suspension, and 2) algae trying to grow. If you don't have iron in your fill water, then you can rule out #1. To test for #2, try testing your chlorine at night after the sun is off the pool and again in the morning before the sun hits the pool. If you lose less than 1 ppm of chlorine in that time, then you can pretty much rule out #2 and assume it's just dirt. If you lose more than 1 ppm chlorine during that time, then you have algae trying to grow and you need to shock the pool.
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