Not sure how you got those numbers, but if they are right, only the TA is low--add Arm&Hammer baking soda to raise it. That's all Alk Up is--Sodium Bicarbonate in a fancy package. Arm and Hammer Washing Soda (in the Yellow box) is the same as pH Up! and other pH raisers--Sodium Carbonate.
You have a vinyl pool. Calcium does NOTHING for vinyl except waste your money and possibly make your pool cloudy, if you have too much.
But those must be pool store numbers because NONE of the kits we use can take those measurements.
FC: We could measure 12.2 or 12.4, but not 12.15. But, if it's between 12 and 12.5 and holding, it's a tad high but the CC is right and the CYA is right, you'll need to raise it to 15 till CC is below .5
CC: Could be .8 or 1. More chlorine to lower this
pH: 7.3 is fine
TA: 21??? I can measure 20 or 30, but not 21. IF your pH is holding fine at 7.3, I think you're ok. If it keeps dropping and you're not using Tri-Chlor pucks, try raising it to 60 first and see if it holds. Then 70, then 80. In theory, you could go as high as 190 with no problem--it's a vinyl pool.
CYA: Again, 42 could be 40 or 50. Either way, FC should be 3 to 6, shock at 15
Calcium: You can measure 120 or 130, but not 126. Either way, don't worry about it. Don't add more calcium, it's a waste.
With those #s, I'd stick to liquid chlorine or bleach for rather than pucks or powders. They all add stuff besides chlorine, which, right now, is all you need. Plus baking soda.
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