PO4 test kits - Hanna VS Salifert

[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...

[Myka]

Originally Posted by 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.

The calcium checker is horrible. It's not your fault. That checker is NOT user friendly, and few people can report consistent, repeatable results.

Originally Posted by GoFish

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

The hot water rinse and drying at the end is to remove any blue residue inside the vial since the blue color (which may or may not actually be visible to you) sticks to the vial, and over time will leave a "stain" that takes some serious scrubbing to remove, and because of the shape of the vial scrubbing is difficult. The tank water rinse at the beginning is to remove any fibers from the drying of the vial before storage. Since tap water could easily throw off the readings I use tank water. I doubt there are any fibers introduced when I clean the top of the vial curing the process as I'm really just putting it gently in the opening and the paper towel wicks any drops out, there isn't much movement of the paper towel.

[Delphinus]

Re. the Calcium checker - what, people have trouble retrieving only a single molecule of tank water? Who could have foreseen that!!!!

[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!'

[Ryanerickson]

I tried mindys method it gets me way lower results, 4-6 ppb so almost none existent I'm also questioning if this method is correct as its not what the instruction say to do,
I also watched a video they did not use this method either.
How did you get this method for testing mindy?

[Delphinus]

Maybe slightly off topic but being that I've been doing a lot of PO4 testing lately, I noticed something. I can tell when I'm about to get a wing nut reading, by when it looks like the colour didn't change at all rather than if it changes more than I expect. Ie. if I see a slight blue tinge to the water then I get a lower reading which tends to be inline with the day to day trend. But if it looks perfectly clear then I'll get a reading that puts me into the "WHOA WHAT HAPPENED IN THE TANK TODAY" territory. (Which of course I repeat the test and usually calm down when the next reading makes more sense).

I am using up a box of older reagents though, so maybe that's part of the issue in my case. I would say I get in the ballpark of 1 in 4, are these wingnut readings that don't make sense.