I just drained around half or more of my pool to lower my CYA. (I performed an AA stain treatment just before draining, so that I could dump some metal also. I'm going to install a Liquidator to get off of the CYA treadmill.)
I added borates in the spring (great stuff!!). The level back then was probably around 50 ppm since I have a roughly 15,000 gallon pool and I just followed the TFP borates "cookbook" which uses a 15,000 gallon pool as an example that yields 50 ppm. After a summer of backwashing and a few vacuumings to waste, test strips and pool store indicated that the borate level was probably down around 40.
Pre-drain CYA level was 108 and CH was around 200 according to my LaMotte ColorQ test kit.
After the drain/fill my LaMotte ColorQ kit (twice) showed a CYA level of 26 (a 76% drop) and the pool store showed a level of 48 (a 56% drop). A LaMotte test strip shows a CYA level somewhere between 0 and 40 (a minimum 63% drop).
The ColorQ and the pool store showed a CH of 120-130 (a 37% drop; but I did brush the epoxy walls, which might have kicked some calcium into the water).
My LaMotte borate test strips show a post-drain/fill reading in the neighborhood of 30, but they are not very precise. The pool store reading on borates was BS so I'm ignoring it.
I'm trying to guestimate my post-drain/fill borates level so that I can figure out how much to add back in. I would have thought that CYA would be the best proxy for the percentage reduction in borates, but I know I didn't drain 76% of the water. (The 56% drop in CYA seems more in line with my eyeball estimate of how much water I drained.)
Is there any problem if borates are too high or are they an "enough is good, more is better" kind of spice?
I could conservatively assume that my current borate level is 45 ppm x 50% drain/fill = 22 ppm or more aggressively assume that the level is 40 ppm x 65% drain/fill = 14 ppm (or split the difference at around 18 ppm). What sayeth the gurus?
Note - I'm going to wait for another week or two after the AA treatment, holding pH at around 7.2, before I start bouncing the pH as I add the 20 Mule Team Borax and acid. I'll also probably add one box and the corresponding amount of acid at a time to minimize the pH swings.