When we took over this pool in our new house, the previous owner had a pool service. They had a PoolRx metal thing in the pump's filter area. Based on what I read here, not a good thing to use so I removed it. We have come to notice that there are some small (1/4" - 1/2") stains on the pool floor & walls. (they were likely there before I removed that PoolRx thing; but we just started noticing the stains.) I tried rubbing them off, thinking they were just dirt, but they are definitely brown stains of some sort.
What caused that? Can they be somewhat easily removed? Is there some 'adjustment' to my checmicals that is needed?