Okay, so my recommended FC is 3 to 7. I checked it this morning using the OTO test block. Color is a perfect match for 5. So I checked it using 25ml FAS-DPD. 5.0 FC, .2 CC. Perfect.
But then I got to wondering....why don't they make a color block with useful FC levels? All I know is if I'm close to 5. If I'm way over, I can usually tell I'm above 5. But is it 7? 8? 10? Who cares if the FC is 1? That's not really useful. Who runs the pool that low? Why not have color blocks at say, 2, 5, 8, 11, 14?
Then I had the thought....if I only put in 3 drops instead of 5, my 5 reading should show up as 3. If I read 5, that should indicate rough 8.3. So I tried it. With three drops it still reads a solid 5.
Sigh.... I don't have the heart to try it with 1 drop, or 2....
Why doesn't someone make a color block with useful FC levels?