Just to add a comment, the trichlor is also what's keeping your pH down to the point that you have to add pH ++--by partial drain and refilling, assuming your fill water has a higher pH than that, you'll be correcting that problem at the same time.

I would highly recommend that you stop using trichlor tabs and dichlor shock for the time being, and switch to something else that will not continue to drive your pH down and your CYA up....most of us use plain, unscented bleach that does not add any unwanted chemicals to your pool--it breaks down into chlorine and salt, which is actually good for your water.

Or you might want to consider a salt water generator--I'm looking at adding one to my pool this year because it will make your pool almost as maintenance-free as it can get!

By the way, welcome to the forum!!

Janet