There's nothing in trichlor is different from what's in dichlor EXCEPT increased acidity. The problem with both dichlor and trichlor is that trying to use those ALONE is likely to end up with pH too low (low enough to be irritating) BEFORE you finish testing. That's why I'd like to clear borax, if possible, BEFORE you start. That way, if the pH drops, you can add borax, without worrying that you may be creating a problem.

Of course, I still think the most likely explanation is the 'voodoo goo' in the Shock Plus.