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[PoolDoc]

pH first!

Add borax, 3 boxes at a time, till you reach 7.0. Then 1 box at a time. Retest your TA *after* your pH reaches 7.4.

Add it slowly, since a borax plug in a pipeline is VERY hard to dissolve. (As long as the flow through your skimmer is not getting 'choked' you'll be fine.)

But . . . when you retest pH, do so using a 50:50 mix of pool water and DISTILLED water. FC=19 is high enough to affect readings with phenol red.
(distilled water at Walmart => www.walmart.com/ip/10315382)

[Traxl]

I wanted to give the pool a little time for the chlorine levels to drop. With my CYA levels, I think I should be running between 3ppm and 6ppm FC.

Here are the latest test results...

FC - 3.5 PPM
CC - 0.5 PPM
PH - 7.2 (Base Demand test - 3 drops to ~7.6)
TA - 40 ppm
CH - 40 ppm
CA - 45~50 ppm

When adding Borax, how long should I wait between application and testing?

[PoolDoc]

When adding Borax, how long should I wait between application and testing?

There's no definite answer; a really 'good' answer would depend on observing circulation in your individual pool.

But, 4 hours of pump 'ON' should be more than enough.