Get a small piece of wax paper and pour the regent onto it then into the vial , its too hard to get it all out of the package any other way . I add it to the vial then shake for a minute to a minute and a half max . I also make sure to clean the vials right after use with ro water . I get quite consistant readings this way.

I think thats a good tip with the wax paper, Im going to try that because its so hard to get it all from packet and not spill some. And 2X on washing with RO water, also a little drying stand works great. Think wine decanter drying stand...

i cut the top off and then tear one side all the way open so I can spread the packet more. then i do the tap and i can get very close to all of it into the vial. it's still quite a pain tho i'm going to try the wax paper idea.

I know, but the difference between 0.10 and 0.17 puts it in the same ballpark. It's not an order of magnitude difference.

Where did the 3 minute rule come from? It takes me longer than 3 minutes to dissolve all the reagent floaties.

The meter shuts off automatically after three minutes. Convenient huh?

I know, but you can pre-mix your vial before you even turn the meter on. That's what I do....

they give you two vials. if they were both equally clean you could in theory zero the meter with the first and already have the second mixed with the reagent. but i'm wondering if the vials being different could mess with the result.

The difference in clarity between the two vials is enough to throw your reading off.

if that's the case and we can't assume that two seemingly identical vials are the same to the meter then perhaps even inserting the same vial back into it but rotating it differently could be a factor too.

Bingo... Which is why the Hanna colorimeters for phosphate get such bad reviews. They are a pretty flawed method if two different vials, etc. interfere with the reliable results. And having an auto-off of three minutes when simply mixing the reagent takes a minimum of two was just poor planning...