I don't know how I lived without this test for so long. You may recall from some of my comments in other threads that I am running my pool with a higher CYA than I have in the past. Hence I need to run a higher FC level as per the Cl/CYA chart.
I have been slowly playing with my SWG settings to see how low of a %'age I can go and still maintain my required 3 - 5 ppm FC levels @ 70 ppm CYA. Well my current plain old DPD test (5 drops of R-0001 % 5 drops of R-0002) only goes up to 5ppm.
I started at 75% and everyday I would lower it (65%, 50%, 35%, 25%, 20% etc) and check FC every night. Well at the higher stages of that test I was always reading 5ppm (which I now know was actually higher).
Fast forward to last night where I had the SWG set to 20% all day. First I pulled out the plain old DPD kit. This was the first time that I could say it wasn't so pink that it was 5ppm or above. But it was clearly darker than the 3.0 mark. So I called it a 4.0
NEXT I pull out the FAS-DPD, which I had never used before in all my years of owning a pool.
- 10ml pool water
- heaping scoop of powder (couldn't believe how bright pink that water turned).
- now started the drops... 1, 2, 3, 4, 5, 6 (start swirling really good), 7, 8 (ooh a little change), 9 (BAM - completely clear).
- 9.0 X .5 = 4.5ppm (couldn't believe the accuracy)
Now onto the CC test:
- 5 drops R-0003 absolutely ZERO change in the clearness of the water
This is the ABSOLUTE first time that I can say with confidence that I have a CC level of 0.0. With my old test, you are supposed to add 5 drops of R-0003 after you obtain your FC level and see if the solution got darker. Well toward the top of that comparator, it's just too subjective. I mean if I am already close to the 5ppm color it is very difficult to determine 'darker'.
With the FAS-DPD, there is no shadow of a doubt. It either changes back to pink or it doesn't. Plain and Simple. Very happy I got this test.
As far as my trial and error with my cell is concerned. I am now going to start increasing the %'age every day so I can get an accurate FC level at those higher settings. Today I set it 25% (A 5% bump). My guess is that I am going to settle in somewhere between 25 - 30% and maintain 5 - 6ppm.