Hanna ULR Phosphorous Reagent Disparity

[MicrobeMan]

Hi All,

I recently purchased a Hanna ULR Phosphorous kit (HI 736) and I've been testing every few days while attempting to lower PO4 in my tank to get rid of GHA. Initially, my PO4 was around .09 PPM (converted) and over the past week or so, I've been working it down. As the kit only came with 6 packets of reagent, I ordered some more online. Today they showed up and I measured 0 PPB phosphorous (new reagent expires 2023). This was surprising as all I've used to reduce it was an ATS and two days ago it was 20PPB (~.06 ppm PO4). I thought this was suspicious so I used my last packet of old reagent (that I got with the device 2 weeks ago and expires 2022) and with the old reagent I got 12 ppb (around .04 ppm PO4).
To verify, I did another replicate using the new reagent and once again, read 0 ppb. Hanna reports that they have an uncertainty of 5 ppb at the low end and obviously, 12 and 0 are more than 5 ppb apart.
I called Hanna and after chatting and experimenting with spiking my sample with hydroponics PO4 additive, I confirmed that the new reagent did react with extremely high levels of PO4 (read too high) but the point is, one of these lots of reagent isn't precise. It may not be completely useless but the difference between .04 and 0 ppm PO4 is pretty important in this hobby.
I expressed these concerns to Hanna technical support and the gentleman sort of blew me off and downplayed the importance of this issue. For all I know, my phosphate could be .1 ppm and the new reagent would still read 0! Conversely, the older stuff could have been off and I've been lowering it far more than I want and I'm now in danger of dinos or hurting my corals.
As suggested by Hanna, I'm going to test a friend's tank water tomorrow and see if I get a reading with this new stuff but I have no more old reagent so I don't have much to compare it to. I'm not confident of what I would do with the results of this test. It seems risky to let my tank get a bit dirtier when it could already have a higher PO4 level than expected.

This post isn't meant to be a roast of Hanna or their customer support as I've had extremely positive interactions with them in the past and typically, they make good stuff but I'm curious if anyone else has had this problem. The old lot number (reads actual numbers of P) is H96 whereas the new stuff (reads 0 in my tank when the old reads numbers) is H100. They're both HI736-25. Anybody have experience with reagent from these two lots?

Any insight or advice would be appreciated!

 

[Copingwithpods]

Having the same issue with the Hanna alk reagents from 2 batches. Pack one reads 8.1 while pack 2 reads 9.4,my redsea shows 8.5 consistently so I'm going with that for now until I figure this out.

 

[MicrobeMan]

Having the same issue with the Hanna alk reagents from 2 batches. Pack one reads 8.1 while pack 2 reads 9.4,my redsea shows 8.5 consistently so I'm going with that for now until I figure this out.

I too had a slight issue with their alk reagents. My readings were about 10 PPM off (samples taken 5 minutes apart) which wasn't terrible since I care much more about stability with alk than the actual number but it was an interesting difference. Over 1 dkh is really not good though( Mine was more like 0.5). I think that the amount of time it takes you to go through the reagent is important too as the older bottle I had had been opened a year ago and I went slowly whereas the new one was fresh but thats 100% anecdotal and with PO4, each reagent is a new packet.

I understand there is uncertainty with testing and I know to always take that into account but it's different when it's far more than what they actually report.