I can't keep chlorine in my pool. 27,500 gals., above ground pool with Hayward cartridge filter system. Checked pool Saturday an had no Chlorine. Added 3 gals of liquid chlorine Friday night after dark. Next day at 9 a.m. it was all gone. Took water sample to local store at it was analyzed 15 mins after sample drawn from pool. Results were as follows. 0 Total and 0 Free Chlorine; PH 7.6, 160 Total Alk; 40 CYA, 230 Hardness. Nitrates detected at less than 2.0 ppm. Put 8 gals of liquid shock into pool with 3 lbs of Clean to Green. Sunday morning took reading and the chlorine was all gone. Tired of sweeping (churning up) algae from pool only to have it return the next day with a vengeance. Hemmoraging money with no results. Haven't had a crystal clear pool all year. Thinking of filling 33' roung pool in with dirt and putting sunflowers in it. Help!