I've been a bit miffed and dissatisfied with the new Hanna Checker phosphate meter that's been all the rage lately. I find the darn thing to be terribly inconsistent in not only the errors is provides but the test results as well. Knowing majority of the errors are of my own, human error, I began doing a little research, looking around here and there and found some info that maybe helpful to my fellow reefers here on Captivereefs.
First thing I found is that not only myself but others are making the mistake of using BOTH vials per individual test......so don't do it. Stay focused and be quick use only on vial per test, the clock is ticking, pause the TV! Below may better clarify why this is a mistake.
Make sure both inside and out are completely clean of debris and finger prints.......get yourself some alcohol wipes next time your at the doctor and or a micro fiber clothe to help keep it clean. Simple swipe under your pit isn't enough. Some store there's in RO/DI water, but most certainly do not leave your test solution in the vial as it is said to stain and or contaminate the glass for future readings.
Something that should have been entered into the directions and was not, god forbid they spent the extra 5 seconds and 3 pennies to do it, is that the vial needs to be placed into the meter in the exact position it was to test for zero. Simply get your self a sharpie and make a line to reference. This is important because there are inconsistencies in the thickness and clarity of the glass used in the vials that can effect the test.
Also I read that it is important to take water from the tank 30 minutes to 1 hour after the lights have been turned off both in the display and in the refugium/sump. This is important to provide the most accurate test of phosphates in the system not being synthesized and or gobbled up by all that nuisance algae you're trying to rid your tank of.
Lastly, not critical but helpful get your self a timer. The thing turns off after 1 minute and 30 seconds after zero is registered. Set it to go off in 1 minute 20 seconds to give you enough time to dissolve as much of the reagent powder as possible and get it in the unit before time expires. Once this is complete reset the timer for 3 minutes to help remind you to actually look at your test results once they are displayed. You only have something like 15 seconds to read the results once displayed. I've wasted about 10 tests by performing other test at the same time and not looking back in time.
Even then you'll still find some inaccurate readings of this tester/meter, much like I have. But hopefully taking these extra precautionary steps will help you get a better more closer idea of where your phates are and or if they have gone up or down.
Hope this helps others who have been tearing there hair out over this thing, and please don't hesitate to add any other helpful tips you might have directly to this thread.