Fluctuating Levels

[tnalaskan]

I am totally perplexed. Since our bout with mustard algae at the beginning of the season I have used the BBB method for our pool. I have been VERY diligent to keep the levels where they should be. Here is my problem. My CYA levels are never the same. (When I get strange levels, I test again to make sure I did it right the first time) Granted, in the past 1 1/2 wks we have had to drain some of the water d/t the tremendous amount of rain we have gotten so I expected it to drop some. Have not used the floating chlorinator with 3 in. tabs in about 1 1/2 weeks. Here are the levels :
7/12- FC-8.0 CC-0 PH-7.4 ALK 70 CYA 70 7/13- FC-5.0 CC-0 PH 7.4 ALK 70 CYA-40 7/15- FC-2.5 CC-0 PH-7.3 CYA-60 added 1 1/2 gal. 6% bleach 7/16-FC-4.0 CC-0 PH-7.2 ALK-60 CYA-35 7/17- FC2.0 CC-0 added 1 gal. bleach 7/18- FC-4.0 cc-0 PH-7.4 ALK-70 CYA-50 added 2qts bleach 7/19- FC-3.5 CC-0.5 PH-7.4 ALK-60 CYA-30
Why is the CYA fluctuating? Pool is crystal clear. Water temps have been 90-94 degrees for the past 2 weeks. Test the water around the same time each evening, 6:30 to 7pm, after the sun is off of the pool. Am I obsessing over the levels? Just don't want to have algae again. Thanks in advance for your input. You guys and gals are the best!

[aylad]

The CYA test, assuming you're using the disappearing dot test, is very subjective. You will find that your results can differ greatly with different angles to the sun, different lighting conditions, and a host of other things. That, along with water drainage, can really play with the numbers. Just try your best to imitate the same testing conditions, each time, so that your results from test to test are as consistent as possible.

[Watermom]

By the way, it is not necessary to run the CYA test every day. You'll use up all your reagents too quickly if you do.

[tnalaskan]

Thanks. I guess I will just bring it up to between 40 and 50 and quit stressing over it.