Sandpaper rough feeling to bottom of pool??

[matt4x4]

Very well balanced.......does that include a hardness test for minerals?
Wrong hardness levels can cause al sorts of issues with plaster pools.

[pairadocs]

Very well balanced.......does that include a hardness test for minerals?
Wrong hardness levels can cause al sorts of issues with plaster pools.

Yes, all is well in that area, checked and double checked by 2 companies.

Anyone able to elaborate on my sandpaper pool plaster problems? cause? solution?

I tried brushing, no effect...