Even though I've had the pool for 10 years, I just discovered this site and decided to go beyond my simple Ph/Chlorine test kit, pool store tests, and advice to "shock weekly." It's taken a little study to understand the relationship between CYA and FC, the difference between stabilized and unstabilized chlorine, and the shock regimen one follows to kill algae.
I am trying to kill some persistent green algae which always appears on the steps and a few other places within days of shocking the pool. Obviously, I have not been shocking properly.
Here are the test results: CH 225, TA 100, pH 7.5, CYA 51. At the time of this test, there had been no shock for some time and FC was 1.61. I've studied the tables and understand that based on my relatively high CYA, I should be maintaining more FC. OK. But the real question concerns checking FC after shock using my K-2006 Test Kit.
To determine the level of FC if you use only a 10ml sample of water, you add R-0871 drop by drop until the sample is clear. Let's say I nail the FC level with my first addition of shock (20 for my type pool); the test would require 40 drops (1 drop = .5 ppm) to clear the water in the test vessel and confirm that I've got 20 ppm FC. Is this correct?
Then the procedure is to maintain the shock at least for the first day (until the overnight test can be done to see if any chlorine consuming contaminants remain..), so I would check in the PM --- let's say FC has dropped some, so only 30 drops of R0871 are needed. Then there is the test in the AM --- another 20 or 30 drops, etc.
Am I describing this correctly? It just seems one is going to go through a LOT of R-0871, and I read other posts where people say they use this test daily or every other day to measure FC.