Hanna checkers

[mrhasan]

For alk, the accuracy of the device keeps me away (+/- 5% of the reading between 4.2 to 14). I keep my alk around 8 so that translates to an inaccuracy of up to +/- 0.4dkh. For a $60 machine, that's unacceptable to me.

Don't have any experience with Ca.

For PO4, I don't love it but I can't hate it either because of all the "guess the shade of green" test, hanna atleast get it "right" to some extend and I don't have to play the shades of green game.