Sandpaper rough feeling to bottom of pool??

[pairadocs]

Our pool is extremely rough. Plaster pool, 5 years old, BBB method.

Noticed it this year for the first time. When I put a mask on and swim down to the bottom to inspect, it looks like sandpaper - a smooth plaster bottom, but with many pebble like pieces of sand allover.

Doesn't seem to brush off...

any suggestions.

and yes, we are very well balanced...

thanks

[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...