Reading test kits, ca in particular?

[Scooterman]

Hey boomer, I've got a guy locally wanting the skinny on how to accurately read his API or other test kits when it comes to when do you consider it at the point your trying to test, as in calcium test kits usually go from pink, purple then to blue & he wants a clear answer as to exactly what do go by when it turns blue, do you go a few more drops or do you read it when it first turns blue?
I told him usually when you first hit blue that is the point you use to figure it out, whatever drops that it takes to get it to make that sudden blue change.
I just want to get the correct answer?

Thanks!!

 

[Boomer]

You are correct Scoot

Maybe a drop more and no more to make sure it is blue but that does not mean add that drop to the count reading. End-Point is End-Point and Blue is End-Point, unless a kit has some color card with a predetermined blue or the instructions tell you other wise. Tell him to ask himself the question of logic, if it turns blue how blue do we let it get.

To be more accurate on Alk, in most kits, and that includes API, many kits do not take the pH low enough for seawater Alk and thus read 10% to low, accept the Salifet, when it works and the SeaChem IIRC

So, the kit reads 9.5 dkh, which = 90 % of the actual Alk

So, the real Alk is 9.5 dkH / 90% = .105 dKH / 1 % x 100% = 10.5 dKH more of a true Alk

Tell him to put the vial down on a white piece of paper and view the color from the top down. And when it is blue, not some shade of purple that is it.

 

[Scooterman]

Thanks to the information & Time Boomer!