Reading test kits

[sfsuphysics]

Ok so today I want to test my alkalinity to a little higher accuracy than my test kit provides. My solution use 20mL of tank water instead of 5mL and that should increase my resolution by a factor of 4 correct?

So I'm adding drops, now each drop = 0.25 dKh.

Problem is I'm now unsure when I'm at my final reading. Due to the increased resolution the color change from blue to yellow is quite a bit more gradual. Do I call it done when I see the first sign of "green" (i.e. mixture of blue and yellow) or do I continue until the color doesn't change anymore? Because that can be quite a few drops difference.

 

[Mr. Ugly]

If the kit counts drops to determine dKh, your resolution improves by factor 4.

I was always taught that the first sign of persistent color change is the titration endpoint. But some test kits go past the first color change to a specific color. Seachem Ca is that way.

I would get/make a test standard and do a titration to see what color change matches the known levels.

If testing dKh, you probably could get a reasonable idea by making an accurate batch of Randy alk buffer, and adding 85ml to 10 gallons of RODI water. That should give 12 dKh.