Hello from Cave Creek AZ!
My entire IG spa (plaster) is stained blue. (about 6ft dia maybe 350 gal)
I suspect it is copper from heat exchanger corrosion.
=>What are my removal options/techniques?
Plaster is about 8 years old. It had been acid washed about a year ago (same reason) - a little too aggressively as some gunite might be peaking through (darker patches). Got one replaster (quartz) quote for ~$2000 (includes possible drain fixture replacements that may be required after chipping)
=> Is this price in the ballpark for PHX AZ?
Water chem neglect is the culprit. My Pentair MiniMax Plus 400 Heat exchanger sprung a leak too but that's a separate story - it's fixed but I want to square away Spa plaster before I start up spa (with new religion and commitment I might add).