Sorry, I was trying to figure out who "Dave66" was, what sort of pool he was working on, and what his skills were.

Anyhow, anything "carbonate" is sort of 'solidified' carbon dioxide -- add acid, and it will fizz. Vinegar will work, but it's easier to see with muriatic acid -- of course, muriatic is harder to work with safely.

But, if you can chip off a bit of scale, put it in a wine glass, and then cover it with white vinegar . . . you should be able to see it no problem. If you don't, add a bit more vinegar, cover the glass with Saran wrap (acetic acid is volatile) and let it sit overnight. If it doesn't fizz, bubble or dissolve . . . it's not "carbonate" based.