Yes, you are correct that you shouldn't worry about the TA nearly as much as the high CYA since the high CYA level is essentially making your chlorine very ineffective. So you have to maintain > 8 ppm chlorine levels until you get your CYA lowered. Technically, your numbers (***uming a Calcium Hardness of 300) give you a saturation index of 0.26 which is not bad (only slightly scaling) so don't worry about the TA.

And to make matters worse, every Tri-Chlor tablet that you use (***uming 8 ounce tablets -- yours may be 6 ounce) adds 2.2 ppm of chlorine but also adds 1.3 ppm of CYA and reduces your pH by 0.03 requiring 4.5 ounces of Soda Ash (Sodium Carbonate or ) or 8.9 ounces of Borax to restore the pH. So you really need to stop using Tri-Chlor tablets and start using liquid chlorine or bleach instead (do not pour liquid chlorine into your feeder or skimmer since it should not mix with the Tri-Chlor directly). You can see how one summer season adding 50 tablets would add 65 ppm of CYA.

I used to use Tri-Chlor tablets myself, in a floating feeder, and after 1-1/2 seasons wound up with CYA over 100 when I had a heck of a time maintaining chlorine levels as the tablets wouldn't dissolve fast enough to give a high enough chlorine level (at least you figured out to use liquid chlorine to supplement). Then I found this site and also investigated pool water chemistry and found that CYA significantly reduces chlorine's effectiveness. A little CYA is good since it helps protect chlorine from breakdown from sunlight, but a lot is not good. I only use liquid chlorine now.

So, bottom line, either ride out this season by maintaining high chlorine levels and hope that the CYA declines over the winter (by the mysterious process we have not yet figured out) or either now or in spring do a drain/refill to reduce the CYA level (which will also reduce TA and CH as well). I ***ume your fill water isn't super-hard water so isn't high in TA and CH. You should probably test your fill water as well so you can predict what will happen when you drain/refill.

Richard