Ben's Lowering Your Alkalinity procedure step 3 says:

Use small doses of acid to lower your pH to just above the lowest value on your testkit -- or 6.6, whichever is higher. Do NOT lower the pH to whatever the lowest value on your kit is! In many cases, if you try to do so, you'll ACTUALLY end up with a much lower pH, which can damage your pool. Instead, make SURE that your pH is at least a little higher than the lowest pH value your kit shows. Also, do NOT try to lower your pH all at once; for all sorts of reasons, it's important to do it gradually!

I'm not putting this here to make you feel bad, but to make sure others reading this know to follow Ben's procedure exactly so that this problem can be avoided in the future. In short, do not target the lowest pH measurable on the pH test, but target one level higher. Since most test kits measure down to 6.8, that usually means using a pH target of 7.0 for this procedure.

Richard