I spent some time searching/reading more on this forum about CYA and possible reasons for it not to go up after adding it -- I've seen comments about losing CYA via water loss (not happening), bacteria converting the CYA to ammonia (don't think that's happening), and a few comments referring to rumors of possible bad batches of CYA (seems possible).
History: When using a solar cover, my pool uses no more than 1 pint to 1 quart of 6% bleach daily. This has been fairly steady. Since it has been too hot to leave the solar cover on, I've been adding more chlorine to make sure FC doesn't go too low after the pool being in full sun all day (no shade at all until the evening). In full sun, I end up using ~5 quarts of 6% bleach daily. After killing off algae from my steps a few weeks ago, the steps are still out & CC is usually 0, but sometimes 0.5 (barely pink) daily. Water is just about glass clear. When I put the cover back on, bleach usage immediately returns to 1 pint to 1 quart. FC has not tested below 4 for the past couple weeks.
My CYA was testing under 30, so I decided to add more. After adding a couple pounds via socks in front of the skimmer, I waited almost two weeks & now the CYA still tests as under 30 & thus hasn't changed. I have the 50ppm CYA standard solution from TFTestkits & confirmed that my testing method resulted in a ~50 ppm reading, so I don't think I'm testing wrong.
I don't think this qualifies as bacteria converting the CYA because Cl usage only goes up when the pool is uncovered in full sun.
Am I missing a reason for the CYA not to budge? It just seems to me like the CYA I have isn't doing much of anything.
The CYA bucket is Nu-Clo brand. I'm tempted to buy some from a different pool store & try that instead of wasting time adding it again & waiting to retest. Now that I think about it, I remember adding 4 lbs of CYA this spring from the same store because of starting with fresh water after the installers fixed a liner issue from last summer's install & that resulted in the initial CYA reading of under 30, which is off the expected 40+ value from the pool calculator.