Yeah, keep up with slugging the borax in there. Your pH got shoved way low by using those tablets. 50K/gal is a lot of water to get to move the pH. It will move, but it might take a while. Using bleach will also help pull your pH up. So, in the future you will be trying to keep your ph down rather than up. Luckily, that's easy to do with muriatic acid.

Michael