The only way to lower cya is to do a partial drain. Concern yourself with that after you get the algae problem zapped. You aren't going to be able to get a good ph reading while your chlorine is so high. Your pool will clear in a couple of days hopefully and you can get one then. As far as how often to dose it with bleach ---- if you can, run a chlorine test in the morning, afternoon and evening. Each time, add enough bleach to raise the cl back up to 20. Having said that, let me also say that you can test as often as you want and each time raise it back up to 20. You won't hurt a thing if you do it more than 3 times a day. Sustaining the high cl reading is the key. The more consistenly you can do that, the quicker the algae will die. Keep us posted how things are going.