Unable to keep chlorine level and CYA level has dropped from 38 to 21 in 1 day.

[lizbyrne2000]

After I removed the iron stains I used a product to remove the iron from the water. I keep chlorine tablets in the skimmer. There are no stains in the pool and the water looks clear and blue. I just can never get a chlorine reading. None of the pool stores around here have the 2006 water tester so I ordered one. I have been checking the PH and Chlorine with a OTO tester. Yesterday I took water samples to 3 different stores and got 3 different results.
1st one said my CYA was 21 a drop from 38 the previous day, they use some machine to test they also said my iron was 0 and chlorine 0 PH 72.

2nd said my CYA was 30 - 50 , Iron .15 & PH 7.8 they used test strips (Which I hate) Chlorine 0

3rd my CYA was 10, Iron 0 & PH 7.2 Chlorine 0 They were the only one's that tested with chemicals.

[ Admin: added image showing these results as a table. ]


I added 6 lbs of stablizer 4 lbs of shock ran filter 24 hrs (which I have been doing) about 1:00 PM tested the next morning chlorine was high by 4:00PM it was gone. The week before I added 4 lbs of stablizer. My pool is 30,000 gallons. HELP