Im having trouble finding an accurate CH number.

Last month I tested the water (with a K2005 kit) and CH was 280. A few weeks later it was 260. I tested it several days ago and the number was 380. I re-tested yesterday and it was 300.

I obviously assume CH can't jump around like that, so it must be a testing error. But one difference between the tests was that when I got the 380 reading, the pH was really high. It was around 8.0 at least. I added acid and it went down to 7.6. When I retested the CH the next day, it was 300.

I know high chlorine can effect pH readings, but does pH effect CH? Water appears clear and no signs of scaling or anything like that. Of course the pool is new so I've been fighting with the pH. And that's why Im wondering if that might be effecting my tests.

Other latest readings..
FC = 4.5
CC = 0
TA = 90
CYA = 40
pH = 7.6
Temp = 80 F
Pool age is almost 3 months and has a SWG.

Thanks for any advice...

High pH is not supposed to affect the CH test. You should make sure that your titrant drops are wholly formed and should wipe the dropper tip with a moist cloth if the drops squirt out from static electricity (otherwise you get too many drops and an artificially high count). Also, with the CH test, you need to wait and stir between drops for some time to ensure thorough mixing (this is where the SpeedStir can really help).