Your CYA will not go up on its own. It has to be testing error.
Was the lighting different from one CYA test to another. It is important to do it in the sun light about the same each time. Read up on testing CYA in other threads....
Your SWG will always have a difficult time "catching up" unless it is way oversized. Use bleach to bring up the FC level needed and then let the SWG maintain.
But will CYA drop 30ppm in a week without a water change? If my testing is accurate then where did it go?
I've read everything I can find on CYA testing and I'm sure I'm doing it right, but for me it is the most difficult test to read.
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