I think dirt on the bottom of a pool is typical of everybody's pool. I can vacuum my pool one evening and by the next day, there is already a little dirt/dust on the bottom again. Of course, as soon as we are in the pool moving around, the dirt gets into the water suspension and you don't see it. Later, when the pool settles down after we are done swimming, it will resettle. Especially in the "tape lines" underneath my liner where the underneath foam padding is taped together. No matter how clean I seem to get it when I vacuum, the next day there is always a little on the pool floor. I have a feeling that is what is happening with your pool as well. BTW -- Welcome to the forum!