Ok, I have a 16 x 32 vinyl above ground with a deep end of 5ft. I have had my pool 13 years. 1st 6 yrs I used baquacil. Had a lot of problems with water mold and pink slime so I switched to bioguard. Been on chlorine for 7 yrs now. I have a chlorine demand and after spending $400.00 dollars so far on pucks, diclor, triclor I still have no free chlorine reading. Test are showing cya up over 150. Pool store are not concerned they just want me to keep addin more shock. I have added 20 Lbs shock so far and still have not beat the demand. I am fed up of pool stores. My pool is clear but I don't like not having free chlorine reading. So after all this.... How do I do a partial drain on my above ground vinyl pool. My goal is to get the cya down to 40-60 and never use pucks, dichlor, triclor again. Is it safe to just vacuum to waste until it is half full and then fill it up again.