Hanna 736 100ppb standard test

m2434

New member
In another thread the question of the Hanna 736 phosphorous checker came up. I can't say with any certainty what the limitations of this checker are, however, I do have the 100ppb phsophourous standard kit. So, using the 0 and 100ppm standards, I am able to do some basic tests. I realize others may be interested in the results, so, I just did 5 tests consecutively. The results were 97, 103, 103, 109, 106. Hanna claims an accuracy of +/- .05 ppb. The results are fairly close and have been other times I have run this test as well. Of course I can't say what the accuracy is at other ranges, however, it seems to be fairly accurate. The 109 was a bit of an outlier, however, given the observed standard deviation, it does seem to be within the manufactures specs, at least using their standard.

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m2434

New member
BTW, before someone points this out, I'll correct myself.... I can't really say it's within the manufactures specs, I can only say I failed to show that it is out of the manufactures specs :lol:. It could prove to be out of spec if I ran more tests. Also, if others have the standard, and can run a similar test, please feel free to post the results, pooled data would certainly be even better.
 

Randy Holmes-Farley

Reef Chemist
Premium Member
Thanks for posting that. It is interesting. :)

Do you know what the standard is? Is it a seawater base, or just fresh water plus phosphate? That and the variability of aquarium water even with all being "seawater" is one of the problems in attaining standards suitable for seawater testing.
 

m2434

New member
Sure, no problem :)

I can't tell you what the standard is based on. And I'm not sure what the correct term is, but it is a pre-prepared "color standard". There is a 0ppb vial for centering the checker and then a 100 vial for testing. I'd think some of the variability would be taken out of the equation by centering the sample? However, this test method, certainly does not give any indication of how well the reagent works with salt water.
Also, just re-reading the fine print, they only certify it is accurate to +/- 10ppb phosphorous. So, certainly I can't say definitively what the limitations are...

Do you know of any good source for a standard that could be mixed with the reagent? I'd be happy to do some more testing if at all practical. I am very interested myself.
 

fcmatt

New member
I bought this standard and was really disappointed with the quality of it.

Mine came in plastic tubes instead of glass which were not exactly scratched up but no
where near as pristine as the glass tubes.

I also saw floating material in the solutions. Like little dust particles or strands of something.

The 100 ppb tube leaked. It was not sealed very well. A very very slow leak but it
would end up getting the outside wet when handling it during the multiple tests i was doing.
The 0 ppb never leaked. This would probably explain why it had more solution in it compared
to the 100 ppb. Also, making sure every bubble was off the tube of the 100 ppb was a real
pain in the rear for some reason. There would be little bubbles if i created them accidentally
and that is how i discovered the leak trying to remove the few stubborn bubbles.

So i pop in the zero tube.. and then pop in the 100 ppb tube i had to be very very careful
to choose sides that were not marked up. I got readings very similar to yours but after
I was done I just tossed it. It made me realize the thing works as claimed but did not
allow me to determine just how well it worked accuracy wise or just how consistent either.
Like I said.. my plastic tubes were not as nice as the glass.

I was sorta hoping I could open the tubes and pour it into my glass vials but how would
I ever know if the plastic tube would act like the glass? Maybe the LED light would go
through it differently and their lab calibration assumes the plastic. I dunno. Either way
I did not have enough 100 ppb liquid to use the glass tube. It did not fill it up high
enough.

Plus.. the darn test tubes had a rubber stopper and rubber cap on it which did not even
fully fit into the tester. You could not even shut the lid fully.

I was also disappointed with the whole +-10 ppb range myself. I was expecting half that at
least.

So in summary.. it was good enough to make sure my checker was not broken but that
was about it.
 

m2434

New member
Interesting, mine seemed quite well sealed and I thought it was glass. Of course, I've tried not to handle it any more than absolutely necessary, so maybe I just didn't notice.

Regardless, I think that is what the standard is primarily intended for, to check to make sure it is working within a reasonable tolerance. I do agree it would be nice if the standard was better than +/- 10 ppb.

Also, to add, I think I mentioned that the checker is claimed to be accurate to +/- 5ppb, however, actually, they claim 5ppb and 5% of the reading. At the levels my tank tests at (usually around 10ppb or so), the 5% is so nominal I don't think about it, but at 100ppb, it does actually matter.

I'm still thinking of a way to test it with a standard. It looks like Hach has standard solution available. If I understand correctly, It seems that the difficulty with saltwater though is removing any background PO4 noise. Most salt mixes probably contain some P.

Removing this may be difficult. It seems that ideally, you would add the reagent to some saltwater, center the checker on this. Then add some P standard to the solution and run the test. I'm not familiar with the chemistry enough to know if this would work, in this order. I don't know if the reagent would still be effective by the time the standard is added for example. I tend to think it wouldn't be reliable, but I don't know.

If not, I was thinking, off the top of my head, the only thing I can think of would be to mix some fresh saltwater. Do a number of tests with the saltwater. And with some saltwater, with added standard to raise the P a certain amount. With this, at lease it would be possible to see if the change was as expected, and look at the variation. It might be a good proxy, or maybe there is a better way I haven't thought of?

Also, there was a PO4 checker review on ************ where they used seachem flourish to create a standard. This would be easier to obtain, but I'm not sure how consistent flourish would be?
 

Randy Holmes-Farley

Reef Chemist
Premium Member
Oh, so this is not a phosphate solution that you add reagent too, but rather just a color standard that gets translated by the machine into a phosphorous reading?
 

m2434

New member
Yup, this is just a color standard. So, you still need to take the manufactures word that the color is an accurate representation of the the reaction with the reagent at that level and that the reagent is prepared properly etc...

Unfortunately, in the end, other than with regards to repeatability, the manufactures specs are the best we can go on. At least without more extensive independent testing.
 

Randy Holmes-Farley

Reef Chemist
Premium Member
OK, I agree that is not much of a test of the accuracy or even the reproducibility, since the sample is exactly the same color every time.
 

m2434

New member
Right, it only show repeatability, not reproducibility. Reproducibility can be tested to some extent by testing the tank water multiple times though, over multiple days. And it's easy for others to do as well. And I do repeat tank tests often as well and the results do tend to be consistent.

I guess there is an important vagueness in the manufactures claimed accuracy though. The don't differentiate between variance and bias. In reality, variance isn't as much of an issue, as I can repeat tests many times if I want, however, bias is.

I'll have to look into those standards. I'm willing to spend some money for the knowledge gained, but there is certainly a limit . I think the methods I mentioned above would be withing that limit though, but not sure about anything else :)
 

m2434

New member
Also, just as another thought. Is it the salinity that is an issue, or more specifically the chemical interactions? If the salinity is the issue, I'm not sure about the purity of the ones sold online, but I would think a pharmacist would be able to make up a fairly pure 35ppt sodium chloride solution for example. Could you then add some PO4 standard to that? Seems like that would be fairly cheap.
 

110galreef

New member
link you provided that the guy did was with the HI 713 Phospate checker, you have the HI 736 (Ultra low phosporus checker)?
Yet you used 100 ppm test solution & got ~ 100ppb readings? (original post)

Was this a typo?
 

m2434

New member
link you provided that the guy did was with the HI 713 Phospate checker, you have the HI 736 (Ultra low phosporus checker)?

Yes, that's correct. According to the manufacture, the 736 should be more accurate at low range than the 713 though. Presumably the same standard he used to test the 713 could be used to test the 736. I'd like to do something similar with the 736, but possibly account for the saltwater if possible.

Yet you used 100 ppm test solution & got ~ 100ppb readings? (original post)
Was this a typo?

Yes, sorry about that not used to talking in ppb. The threads title is correct, though, it is 100ppb.
 

m2434

New member
Hanna Tank Water test

Hanna Tank Water test

Ok, just for kicks I ran 5 consecutive tests on my tank water. Actually 7, as the first gave a vial inverted error (although it wasn't) the second I messed up, by not holding down the button long enough after adding the reagent.

For the 3rd through 7th, here are the results. According to the documentation it is accurate to 5ppb phosphorous +/- 5% of the reading. Although they claimed +/- 10ppb +/- 5% of the reading and latter lowered the estimate.

This test was more consistent with +/- 10ppb, as the tests ranged from 0 to 20. Of course, this is more of a real world test, not so controlled like the standard test I did before. Therefore I can't rule out testing error, bubble, particulate material etc... And, of course this only takes into account random error, not bias. So, I can't draw any independent conclusions about the accuracy without a better standard. Randy's point is taken, the color standard test is of limited value. I'm still looking into some standard
options.

However, Randy, I take the silence to mean you don't think my alternatives to the seawater standard are a reasonable idea?


Anyways, the results, in ppb P were 0, 11, 1, 20, 12. Converting to ppm phosphate, this would be 0, .0337, .003, .061, .037. Also, my camera died after the 3rd test LOL, so I had to grab my gfs cell phone. I have to say that the new iphone camera is pretty good, but that's a another test :)

0ppb
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11ppb
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1ppb
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20ppb
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12ppb
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fcmatt

New member
on repeated tests of my tank water i never had such a variation in results. often times they
would come out exactly the same... like 8 ppb and then 8 ppb when running a test twice.
 

m2434

New member
on repeated tests of my tank water i never had such a variation in results. often times they
would come out exactly the same... like 8 ppb and then 8 ppb when running a test twice.


Good to know. I can post my results, but that's just one particular device, on one tank, or color standard etc... Definitely more helpful if others share their own results.

I'm sure there is a lot of variation, with different meters, different tanks, test procedures etc... I mean it's fifty bucks, measuring ppb. So, when I say I think it's very good, of course that's very good with regards to other hobby test equipment. For hobby equipment, based on the manufactures claims, it's exceptional. I don't think many if any hobbyists have the ability to rigorously test it's accuracy, hopefully we can get a rough idea at least.
 

Randy Holmes-Farley

Reef Chemist
Premium Member
However, Randy, I take the silence to mean you don't think my alternatives to the seawater standard are a reasonable idea?

Sorry, been busy with other projects.

A Hach phosphate standard, especially spiked into tank water to get several known concentrations rather than tested alone is a good test. :)
 
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