Thanks to both Watermom and PoolDoc/Ben for the replies. Our pool is 12,000 gallons and six years old. We have owned the house for three years in August this year. We use stabilized chlorine tablets in an inline feeder. Standard Pentair Clean and Clear Plus cartridge filters plus the new Intelliflo variable speed pump. Our pH is usually around 7.2. We used to need to add acid to bring the pH down. Lately we have been having to add powder to bring the pH up. The mustard algae will start if the chlorine tests below 5. We can usually keep the algae away with chlorine around 8. You are correct in that we have been taught to believe that anything above 5 on the chlorine test is "high". We don't use strips. We use the Taylor Basic DPD test kit. From reading your forum we purchased the HTH 6 way test kit from Walmart so we could look at the CYA level. The test we did showed CYA at 150 or so. We then took a water sample to the pool store. They did use a strip and said the CYA was 110. We are wondering if we should abandon the stabilized chlorine approach and use bleach and Borax as you have written about? Then, as you recommend, let the CYA level drop on it's own over the next few seasons? Thanks for your help.