The spa was replastered and filled with tap water. Two or three days later no problems or discolorations were noted. At that time I was told to put two gallons of acid into the spa and to brush the plaster. I put in only one gallon thinking that even that was way too much but what do I know? Maybe the acid is used up by the plaster in the curing process? 5 ounces of cyanuric acid were also added along with 1/3 lb. chlorine shock. 24 hours later I decided that this was way too much acid and added a pound or two of soda ash to raise the pH to 7.6. The plaster now was exhibiting light sky blue discoloration (copper from heater?) along with random shaped areas that were turning a uniform much darker blue. 24 hours later, the plaster looks terrible with random patches of what looked like blackish green algae. Wire brushing some of the dark patches seemed to remove a surface layer of plaster leaving a white splotch. 24 hours later more darker spots. Did the acid do this damage?