OK, first I need to say the "BBB" method is an approach, not a set of chemicals. (It's my idea, so I get to say what it means! ) Bleach, borax and baking soda just happened to be what's available at the grocery store in generic form. "CHBB" is not as catchy, but if cal hypo were available at the grocery store, that page could have been titled "Cal hypo, borax, and baking soda".

Or, maybe not. My boys used to roll their eyes at me, while griping that I always alliterated at them, accidentally or not, when instructing them in life lessons.
-- Lisa, be nice! They really did! Now, they often alliterate, too, driving Susan nuts, since her alliterative achievements are almost always unimpressive. --

Seriously, BBB is not, fundamentally, about bleach. Bleach was just what was available.

Anyhow, your CYA hasn't disappeared. The only way it can do so is if you drain and refill, or if you have bacterial growth (equal major biofilms, AKA seriously slimy sidewalls*) that can biodegrade the CYA into urea and ammonia.

Most likely the difference is a testing discrepancy. Have test strips been used for any of your testing? I'm not sure if they've gotten better, but I know that when I tested several brands of test strips 4 or 5 years ago, the CYA test results were pretty hopeless.


Ben



* See, I just can't stop myself. Now, no doubt, there will be a new acronym: "Yes, you must have had a bad case of SSS over the winter -- that's why your CYA is missing".