The CYA is the trickiest test to perform. As others on here have suggested, it's best to do the test outdoors in bright sunlight. I always stand with my back to the sun and hold the testing vial with only my thumb and forefinger at waist level in the shade of my body. I pour to each line of 10 starting with 100. I don't stare at the dot, just glance at it. If I see it, I pour to 90 and repeat. If you just stare at the dot continuously, your mind can play tricks on you and make you believe that you see the dot. Always glance and look away. That seems to work best for me. Once the dot disappears, you have your CYA number.
For draining, I've found that a sump pump or utility pump works great and doesn't put the pool equipment in jeopardy of being damaged. You can rent one at Home Depot or buy your own. I bought one from Amazon for $50 and I really like it.
Once you get your CYA level down to around 50 with a 40-50% drain, SLAMming the pool will be much easier. You'll raise your FC level up to the 16-20 PPM range and keep it there by testing every few hours and adding whatever amount you have lost with liquid chlorine. Do not use any more solid forms of chlorine because those will raise your CYA level with every dosage. That's probably what got your CYA so high to begin with. Stick with liquid chlorine only. It does not add any CYA at all.
