The CYA test is hard to read accurately so variation of 10 or 15 ppm is not unusual and doesn't mean it actually dropped. Going two weeks without any maintenance on the pool is a big stretch. At least with your low chlorine demand you could probably load up enough Trichlor pucks/tabs to last long enough assuming you turn down the feeder slats appropriately. Yes, you could raise your TA level which will help keep the pH up in spite of the Trichlor assuming the pool remains uncovered. Over two weeks, with 80 ppm TA and starting with a pH of 7.8 (I wouldn't go to 8.0 as you might get some metal staining if you have some metal ions in the water) you would end up as low as 7.05 in pH though in practice it will likely be higher due to carbon dioxide outgassing -- a guess would be 7.2. So that might be OK. A TA of 100 ppm would end up no lower than 7.1 in pH (this all assumes 1 ppm FC per day added from the Trichlor and consumed/used). So you can probably raise the TA to the 80-100 ppm range, load up the Trichlor tabs, and be OK, but if the feeder is set too high then you might run out while if it is set too low then the chlorine level could get too low. It's dicey and tricky to get right which is why automated systems and especially helpful neighbors work out better.
If you were always going to use Trichlor, then your TA could be at 120 ppm or even higher, but there's not much sense in getting it that high if you are going back to chlorinating liquid or bleach upon your return.
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