I found this tid bit online...If this is true, then maybe we should be slamming and circulating our water first before checking CYA.
Pool / chlorine conditioner should only be added after properly testing its level. As I noted in the previous post, you should have your pool water tested about 3 to 5 days AFTER the pool has been open and operating to thoroughly "mix" and distribute everything that is in the pool's water - even last year's CYA; it didn't go anywhere over the winter. In truth, the water that contains the CYA is more dense than the rest of the water and therefore sinks to the bottom of the pool. That's why it's so necessary to circulate and filter the pool water for several days before having it professionally tested (most home test kits or strips don't test for CYA).