Quote Originally Posted by heyred52 View Post
...The line on the back of the CYA test tube says 1.8...
I found the line you're talking about! It's molded into the side of my comparator as well. It's actually a measure of ml, mine reads 1.8, 4.5, and 9. Trouble is, this is well short of scale for CYA, you probably can't even see the level on the front CYA scale.

This indicates that your CYA is much higher. You can use the dilution method to get an approximate measure of high CYA. Dilute one pool water with 2 parts tap water (1/4 Cup pool water and 1/2 Cup tap water) perform the CYA test on this diluted sample and multiply the result by 3. If you're still above 100 CYA with the dilute sample, try 1/4 Cup pool water with 1-1/4 Cups tap water and multiply the result by 6.