See the 'sticky' in the alk forum for procedure for lowering alk.

Chlorine - I'm assuming when you say extra strength, you mean 'ultra' which is 6%. Regular is 5.25%. Either is fine to use.

CYA is stabilizer or sometimes it is called conditioner. Some people can add it and it lasts from season to season. Others, like me, have to re-add it every spring.

Hope this helps.