I've been trying to balance my 22k gallon pool (been sitting covered for 2 years), and have a strange situation. Chlorine appears to disappear very fast. A few days ago, I used 8 bags of super shock and the cl level tested 0 the next morning. So tonight I shocked it again - 4 gallons of liquid chlorine, and 2 hours later I expected a cl level above 10 but it tested as 1!
pH is still pretty high, looks like 8.5 or so, will get some more pH decreaser to get that down tomorrow. so pH is ~8.5, CYA is ~50, alkalinity is ~80.
There does appear to be a bunch of algae though - water tint is quite noticeably green. Has been swept/brushed.