PO4 test kits - Hanna VS Salifert

[gregzz4]

Meant to reply last week but got busy and forgot.

Mindy, have you performed back to back tests to see if your procedure gives you a different reading than the instructions' procedure would?
One test your way and one test the Hanna way?

I ask because you're supposed to;
Swirl or whatever for 2 minutes, then insert the cuvette and hold the button to start the 3 minute countdown.
I double-checked; their online video shows it this way.

What I gather is the full countdown allows any un-dissolved powder to settle before it takes the reading.

I use the regular model HI713 and find it's always been reliable by doing the above, even with back to back tests - ya know, for those times when it reads 'what the hell? It can't be that high!'