My first thought is that it may be pollen--do you have trees nearby the pool? Or construction going on in your area? If so, vacuuming or daily brushing to stir the stuff up in the water and let the filter take it out is about all you can do.

It's also possible that it's mustard algae--what is your CYA level, and what is your average chlorine level? Does the yellow powder form on the sides of the pool or just the bottom? And does it appear to increase in amount over a few days?

Janet