Does Alkalinity Cause pH To Increase Faster?

[chem geek]

You are fine so long as you don't have any exposed grout in tile or anything like that -- it sounds like there isn't any and of course there is no plaster/gunite. So "corrosion" in the sense of dissolving calcium carbonate from plaster is not possible for you (aren't your pool walls vinyl?). As for "corrosion" of metal, that is very unlikely at your pH so long as you keep it well above 7.0 (7.4 is fine). You'd have to have a heck of a lot of dissolved oxygen in your pool to corrode metal at this higher pH so I wouldn't worry about that. For a little extra safety, you can do as you suggest and add some more calcium by using Cal-Hypo for a while, but I don't think that's necessary.

Technically, the fact that you've been running with virtually no calcium means that the TA level doesn't really matter -- you are already corrosive for calcium carbonate, but that isn't relevant for vinyl pools with no grout/plaster/gunite exposed to water.

As for salt, it is technically more corrosive for metal since it increases conductivity, but again this isn't a problem in your situation because you don't have a lot of dissolved oxygen in your water and you are keeping the pH alkaline (> 7.0). If you had some sort of iron parts exposed to your pool, then slow rust could happen, but generally any metal designed to be exposed to pool water is either stainless or galvanized steel which resists corrosion or is copper (in heaters) which doesn't corrode as readily as iron (raw steel).

Richard