@brandon429 could probably explain the science behind it all better but ill add my experiences with the API kit.
Does it register low enough amounts needed in reef tank? And how could you tell based on the color or ranges offered on the test strip?
I'm really not sure how accurate it actually is in comparison to actual icp test or running seneye on my system.
I can tell you I'd only use it to guage high levels cycling a non bottle bac cycled system and that would only be for reference of i didnt have any other choice.
That goes for the entire Master API test kit.
I have gotten API Nitrates test kit to test close to red sea kit maybe 1 out of 5X.
Not sure if it leaking beakers, inaccuracy of drops, following directions to the T.
Or if there are too many variables in what I mentioned for it to just fail if you dont get one of the right.
API could stream line and change things up a bit for sure. Maybe go after those lower levels and make kits more user friendly for reefers.
Until that happens I will not be trusting API kits anytime soon.
I got a bad Nitrate kit out of box brand new and it almost cost me my entire reef fixing it.
Peace