Test results after partial drain. Next step?

Since I had a CYA of over 100 and TH of 500 I decided to drain the pool last night. I took the water level down to 28 inches which is almost halfway. Finished refilling it today around 11:30 am then added a 1 gal 46 oz bottle of 6% bleach.

Before this I was having to add at least 2 of these bottles every night just to get a chlorine reading of any kind.

At around 5 pm I tested the TC at 5. I did a complete test around 10 pm and got the following.

TC 3
Ph 7.2
CYA 80 (was expecting this to fall quite a bit more)
TH 280
TA 180

I am not sure how accurate this HTH 5 way kit is, however, my results tend to vary significantly to the pool stores tests in some areas.

BTW. I have a 20,000 gal AG pool

Your test results don't look too bad, except TC of 3 isn't high enough for CYA of 80--you should have it closer to 5 or 6. Your TA is still a tad high,but in a vinyl pool with the lowered calcium, it shouldn't cause you a problem. I wouldn't use cal-hypo products to chlorinate/shock with, though, because it'll make your Ca go up again and the high Alk can cause you some cloudy water problems.

Janet