PO4 test kits - Hanna VS Salifert

[GoFish]

Just picked up a new Hanna ULR Phosphorus kit and tested tank. It says 72, so after some math (72 x 3.066 / 1000 = 0.221)
Then tested with Salifert kit and as always it shows only a slight hint of blue. Somewhere in the range of 0.00 - 0.03.
But based on what the Hanna ULR shows the Salifert kit should be showing a really blue test result.

Using only Salifert for the last couple years I've always had consistent test results.

Just did some major water changes to a new salt brand over the last week and tested last night with Hanna only and its down to .23 ppb (0.07 ppm). Haven't cross checked this with Salifert yet but assuming that will still show low

What should I trust more, Hanna or Salifert?

[Craigdillman]

Hanna is much much more accurate, it uses digital "eye" to read to color and doesnt rely on you "guessing" what shade of light blue the color is

Also the hanna ULR mesures in ppb then you convert it to ppm ,

[GoFish]

Makes sense. Just wondering why the Hanna says .221 ppm at the same time the Salifert has barely even a hint of blue in the range of 0.00-0.03 where it's should be showing a darker colour. I'm not a fan of the colour guessing game with Salifert but positive the shade is no darker than 0.03, let alone in the .1 - .25 range

I'll carry on using the ULR, I just thought the 2 were similar in accuracy

[Myka]

Could you describe in detail how you performed the test? I would expect the tests to read closer, and suspect you're doing something "off".

[GoFish]

Which test do you want the details of? I do something different than the directions say on both, the Salifert I stir the sample after adding the powder instead of swirling using the opposite end of the spoon that's rinsed (tap water) and dried very well with a new piece of paper towel. I read it using white light after 2-3 mins, either outside light if it's day time or a white fluorescent light in the living room.

And with the Hanna I don't shake it for 2 minutes, instead for 1 minute until the powder is dissolved and then hold the button for the 3 minute timer. I make sure there's no air bubbles inside the vial and keep the vial facing the same direction (10ml facing forward) for both the calibration and test, then rinse the vial with RO (using a syringe that's only ever used for this purpose) and leave the cap off when put back in the case to let it dry for next time. I found with the standard PO4 Hanna checker I used to have that if I shook the sample for 2 minutes the checker would turn off, not sure if the current versions still have this 2 min/off feature

[Delphinus]

If you get consistent readings with the Hanna checker using the 3 minute timer as you describe then I'd feel fairly confident in its numbers. Assuming of course you have newish reagents - if memory serves there was a time period that there were bad batches of reagents (fairly easy to confirm if you had one of the bad batches - just do 2 tests in a row and see if the #'s match well enough or not).

Not sure how this applies to Salifert's PO4 test kit but I noticed that with the Mg test kit (which is a titration based test kit rather than a colour comparison, so this might be an apples-to-oranges comparison) that the reagents would expire and then you wouldn't get good readings anymore. So if the test kit is more than say a year old, I'd consider replacing it.

If in doubt though, I think repeatability is the real pathway to figuring out which is the more trustworthy result, if you know someone who has a third test kit that you could ask for a test, see if you can get a value that corroborates one for you over the other..

[Myka]

Originally Posted by GoFish

And with the Hanna I don't shake it for 2 minutes, instead for 1 minute until the powder is dissolved and then hold the button for the 3 minute timer. I make sure there's no air bubbles inside the vial and keep the vial facing the same direction (10ml facing forward) for both the calibration and test, then rinse the vial with RO (using a syringe that's only ever used for this purpose) and leave the cap off when put back in the case to let it dry for next time. I found with the standard PO4 Hanna checker I used to have that if I shook the sample for 2 minutes the checker would turn off, not sure if the current versions still have this 2 min/off feature

The ULR checker needs to be mixed for 2 minutes before starting the 3 minute countdown. It needs 5 minutes of development. The checker allows for this. I'd also suggest you do not shake the vial, but tilt it back and forth to mix because microbubbles in the vial will mess up the readings, so will fingerprints or water marks on the outside of the vial. Dried tap water inside the vial from your last rinse will often give you false high readings too.

Here's a very detailed description of how I perform the test:

I use a syringe to fill the vial with a couple mL of tank water, shake vigorously, then empty it and shake as much water out as possible. If there are drops left near the top of the vial I will use a bit of paper towel to get them. Then I add tank water to the 10 mL mark (bottom of the water's curve), cap it. I get the reagent packet ready (so it's quicker) by flicking all the powder down into one corner, then cut off two sides, and squish it open. I clean the outside of the vial with a microfiber cloth. Then I turn on the checker, wait for "C1". Insert the vial with the "10" on the vial lined up with a mark I put on the top of the checker, close lid, set the checker down. Hit the button. Wait for "C2". Add the reagent packet, cap the vial and gently tilt it side to side for 2 mins (I time it). Hold down the button on the checker until it starts the 3 min countdown. When there's about 1 min left, I turn the vial a few times, make sure there are no air bubble on the vial sides, clean the vial with the microfiber cloth again, and insert the vial into the checker, close the lid and wait for the reading (there's about 45 seconds remaining when I insert the vial). Once I get a reading I immediately take the vial to the sink and rinse it repeatedly with water that is as hot as I can stand, using my thumb to seal water inside it and shaking it vigorously. I also rinse the lid. Afterwards I rinse it in RO/DI water, and shake it out vigorously.

[Myka]

I don't think that makes a difference. I just do that to make sure all he bubbles are out. What difference would it make?

[Ryanerickson]

Difference for me was lower results with your method to me it looks like the powder mixes better with the longer time frame to work with it .

[gregzz4]

Originally Posted by Ryanerickson

Difference for me was lower results with your method to me it looks like the powder mixes better with the longer time frame to work with it .

Mhmm
I'm sure Hanna has a reason for the 3 minutes, but who am I to question it?
I think I'll stick with the Mfg methods
Sorry Mindy. I trust and love all your input/insight/knowledge - it's priceless. But in this case, nah