What an excellent site!
It's been obvious to me for a while that my CYA is way too high, through using dichlor for ages. Only through reading this site did I find that out. I just ordered a kit with a CYA test, but already I'm sure: adding yet more dichlor or even hypo barely registers chlorine on the Cl test, and the algae won't die! No problem with pH: very close to 7.2 with small monthly doses of carbonate. So, two suggestions/questions (for comment please).
1) Reducing the CYA (don't know the level yet, probably way over 100)... I doubt draining is possible for most vinyl pools, so I did the step-wise arithmetic for my pool, 16 x 32 rectangular. Pumping out a manageable 15 inches comes to about 5K gal. After draining, refill to skimmer. Repeating this three times--at the cost of 15K gal of fresh water--will reduce the concn of dissolved stuff by about 55%. Possibly more if you pump only from the drain and point the refill hose to the surface. When I do it and have the CYA numbers I'll let you know how it goes.
2) What's the consensus on optimum CYA for reasonable Cl buffering: around 30, or less?
3) Assuming I use mostly sodium hypochlorite (bleach) to shock and chlorinate after reducing the CYA, what acid should I use to neutralize that: dry bisulfate or muriatic (sulfuric)?
4) Does CYA ever go away/degrade, or am I stuck with it? (Of course every time I backwash some water goes out the drain, and more is lost on closing and reopening the pool. All of that is replaced by rain or from the hose, probably about 5K gal per year.)
5) I'm probably missing something else important...please inform!