You know, I've been using the FAS-DPD test for ten years and I have RARELY had to add more than one scoop of FAS-DPD powder. The key is, if it's good and pink, you have enough. Adding more simply wastes re-agent.

There's a much simpler way to get your FC level. I add one drop and say to myself "Point 5". The next drop I say to myself "1", then "1 point 5" then "2" then "2 point 5" etc, until the water turns clear. I put the test cell on something white, usually the inside cover of my old PS233 kit box to ensure there's no pink left.

The, after I add the R-0003, I repeat the process. "point 5", etc. (I think I once got to "1 point 5", a long time ago).

TC = FC + CC.

Carl