chem geek wrote:If you add a hypochorite source of chlorine and the pool turns color almost right away, then that isn't algae but is metals precipitating out of solution at least partly due to the increasing pH since adding a hypochlorite source of chlorine increases pH upon addition. If you then increased the pH further, you just made the problem even worse. Adding acid to lower the pH would have at least put some of the metal back into solution after which point you could add a metal sequestrant to prevent it coming out again.
Has this pool used copper-based algaecides? Or did it use Trichlor pucks in the skimmer perhaps? The former would add copper to the pool and the latter would make the pool very acidic. Zero TA means the pH is below 4.5 which is quite low. So perhaps copper from the heat exchanger got dissolved.
The earlier post about adding more chlorine clearing up copper won't work. Chlorine is great for clearing up algae, but it won't fix a metal problem.
chem geek wrote:I can find nothing about high TA resulting in a clear solution. Are you using test strips? What kind of test kit are you using? I assumed you were using a good test kit such as the drop-based Taylor K-2006 shown here. The TA test normally goes from green to red so if initially red then that's a TA of zero and a pH below 4.5 which is what I thought you were describing. At high halogen levels, the TA test can go from blue to yellow, but it shouldn't be clear.
Others will have to comment on the paint.