You might find that your pH is more stable if you would raise your TA a bit to the 100-120 range. The lower TA is recommended for non-stabilized chlorine sources, but with the stabilized ones, the higher TA seems to keep pH more stable. I can't explain chemically why this is, but if you want a full explanation, I can get Waterbear, Chem-Geek, Pooldoc, or some of the other chemistry-types to explain it. Anyway--I don't know anything about the BIO-DEX product you used, but it's possible that either it or the dissolved scale is part of the problem too.

Also, any form of aeration will make the pH rise--do you have waterfalls, fountains, spillovers, etc? Are your return eyeballs pointed upward so they rifle the surface of the water?