New with pool CYA question

[BlackGT]

I want to purchase a chlorinator but I have resd where that along with tablets will effect the CYA in the water. I drain between 6 to 8 inches during the winter months, and I have a DE filter so i bsckwash the filter once a month. Is that good enough to dilute the water and not deal with algae years down the line?

Also, if I add algeacide one week, with a pound of shock the following week, will that also help keep it in check?

I have an above ground pool circular pool I believe 21 feet and approximately 15000 gallons.

Thank you in advance.