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..

[GoFish]

Well this is slightly embarrassing. I just checked the Salifert PO4 kit and it expired in 08.16... could swear I checked all 4 boxes before Boxing Day And they were all good from 2018-2020 but for some reason had 2 Alk kits together and the PO4 was on a different shelf

Anyway, pointless technical thread question with an expired kit

However I may have an isssue...
Just did 2 back to back tests with the Hanna and got 125ppb (.38ppm) and then 114ppb (.35ppm). Might be more inaccurate than it's suppose to be. Instructions say within ±5 ppb ±5% of reading. It was 23ppb (.07) last night! Will need to do some research into this. The Salifert still shows much lower (but it's expired, interesting to know anyways)

[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.

[Potatohead]

The Hanna checker works and it is accurate, however you need to be very, very diligent about test procedure and the vials need to be spotless.

What I do is;

- Cut open one of the reagent packs and make sure there is none stuck in the corners, etc. Fold so one long edge goes into a V shape.
- Turn on checker, fill vial with tank water. Wipe with a cotton towel to dry, then a microfibre towel to remove streaks/debris. When very clean, put in checker.
- When C2 comes I pull the vial, carefully put in reagent, shake (gently) for a 100 count. Re-do the towel thing, shake a few more times to get any bubbles stuck on the vial to rise to the top, then put it back in the checker for three minute countdown. Keep in mind to do all this you only have three minutes or the checker will power off.

After reading Myka's post, seems pretty similar.

I have had my complaints of this checker in the past, but since using this method and making sure the vials are spotless, it has been very consistent.

[GoFish]

Well may need to work in my precision testing skills just a touch. I learned from having the calcium checker that these things can be super finicky. I was never able to get anywhere near consistent back to back readings with the calcium checker so ended up selling it and sticking with Salifert.

Forgot to mention I do a couple extra things mentioned in the last couple posts with some slight differences. The Hanna vials gets rinsed with tank water before use if I remember, but I feel this is a bit of a waste of time seeing as how they get rinsed with RODI before being put away. Definitely in between test if done at the same time to double check. I also make sure there are no finger prints by giving it a good polish with the inside of my t-shirt usually and check for fibres on the outside. I give the vial a good shake for 1 minute until all crystals are dissolved, and yes it creates air bubbles, but to remedy this I spin the vial horizontally and allow the big bubble inside to dissipate the micro bubbles. If there's some micro bubbles stuck, it gets a tap on the counter and some more rolling. Until they're all gone.
And with the regent pack it gets shaken and flicked a bunch of times while holding one corner upwards, 2 sides cut along the dotted line and the open the flap by pressing inwards from the sides and at no point are there any fingers or anything touching the inside silver lining of the packet. Then a vee shape is formed, powder is dumped, pack is flicked until there no more powder left. Well there's a bit of powder residue left but that near impossible to remove. It's consistent anyway

Potatohead & Mindy: May put a microfibre towel with the checkers from now on, good idea.
Mindy: Not sure about drying the vial inside with paper towel before testing, i'd wonder about getting fibres left behind in the vial? Good call on leaving the vial out for the 3 minutes countdown to give it one more shake, will try this. Do you think rinsing it with hot water makes any difference? I just use cold usually

And at the end of the day I'm not expecting exact back to back numbers, the 8 percent difference last night is fine with me. Just trying to get in the low range to help combat tiny bits of algae that wil never completely go away. Would love to see anything below ten ppb right now, which is what the Salifert is always giving the result for...