Question about Plaster.

Hi All,
I’m Newbie with a 32X14 IG Gunite pool around 22 000 gallon. The pool was finished last fall and we filled it in November. I started brushing the pool 3 to 4 times a day for around 4 weeks and we closed on the 22nd of December. The plaster surface was nice a smooth so I felt pretty good about the work I have done. Three month later we took the cover of and the water level went down to 18 inch under the tile line. The surface of my plaster is now very rough and the service dealer made a command that he had never seen this that bad and that it might be a problem with the plaster mix.

How can I find out if the plaster is from a poor quality??

Guido

PS
I have a lot of problems with this pool. Leaking bad coping and things like that if now the plaster is bad as well I will get ……