Odd it turned brown instead of being blue-first I've heard of that. May have been a reaction with the water source used to make the mix. Test your house water for copper, iron and manganese.

If they acid washed with a strong solution of acid it may well have destroyed the finish. Were you given proper guidelines for start up procedure regarding water balance after the pool was filled? Most plaster finishes will fail because of neglect and improper water balance in the first 2 weeks. It's paramount the water chemistry is balanced and the surface is brushed for a week period 2-3 times per day.

The prep work and the application procedure may not have been followed correctly also.

Put enough crystals in? Diamond Brite is made in batches at the factory and there is no need to add "crystals". There's a good chance if the factory mix is altered, it will void the manufacturers warranty.

There should be absolutely no pitting!

I would call SGM, Southern Grout and Mortar, makers of Diamond Brite and speak with a tech advisor and tell them of your situation.