Alkalinity Standards and Hanna Alk Checkers

[Dkeller_nc]

I'm thinking about getting one of the Hanna Marine Alkalinity checkers to replace the Salifert titration test. Hanna makes two of these - one's the HI772, and one's the HI755. I'm interpreting that the only difference between these two colorimeters is that the HI772 reads in dKH, and the HI755 reads in ppm, but otherwise the principle of the test remains the same.

My purpose for doing this is to increase the precision of my alkalinity determinations. The Salifert test yields a precision of (at best) +/- 0.3 dKH, and in actual use, the precision's probably no better than +/- 0.6 dKH because the actual endpoint is somewhat open to interpretation.

However, I'm aware that precision isn't the same as accuracy, so I'd like to get analyzed standards with the Hanna. It appears that Hanna's HI755-11 standard set is intended for the HI755, while they sell another standard set (the HI772-11) for the HI772 meter. Does anyone know why there would be two separate standard sets? I'm interpreting (perhaps incorrectly) that the wavelength for the two colorimeters is identical, so it's puzzling why they would supply two different calibration sets.

I should note that I have the equipment, reagents and knowledge to do my own highly accurate alkalinity titrations using a standardized HCl solution, buret, pH meter and stir plate. So one solution to the accuracy question would be to simply compare the Hanna reading to a titration of the same sample. But that's a bit inconvenient, so if anyone has thoughts about these Hanna calibration sets, I'm all ears.

 

[Gareth elliott]

Following as i do not actually know the answer [emoji23] but heres a bump.

 

[JimWelsh]

But that's a bit inconvenient

Just do it!

 

[Randy Holmes-Farley Verified Community Expert]

I should note that I have the equipment, reagents and knowledge to do my own highly accurate alkalinity titrations using a standardized HCl solution, buret, pH meter and stir plate. So one solution to the accuracy question would be to simply compare the Hanna reading to a titration of the same sample. But that's a bit inconvenient, so if anyone has thoughts about these Hanna calibration sets, I'm all ears.

Bear in mind that the Hanna "standards" are simply color standards, not any sort of test that evaluates the method accuracy in measuring seawater alkalinity. It's a minimal hurdle that, IMO, isn't that useful since it may convey a false sense of assurance.

 

[Oldreefer44]

For what it's worth: Had an issue with differing results between Red Sea, Salifert and Hanna in testing DKH. Red Sea and Salifert both agreed at 7.8. Hanna results were 5.8. Sent a water sample out to ATI. their lab agreed with Hanna at 5.8. Have since raised it via dosing to 8.2 using Hanna results as the basis and it is obvious that just about everything in my tank is "happier".

 

[Dan_P]

I'm thinking about getting one of the Hanna Marine Alkalinity checkers to replace the Salifert titration test. Hanna makes two of these - one's the HI772, and one's the HI755. I'm interpreting that the only difference between these two colorimeters is that the HI772 reads in dKH, and the HI755 reads in ppm, but otherwise the principle of the test remains the same.

My purpose for doing this is to increase the precision of my alkalinity determinations. The Salifert test yields a precision of (at best) +/- 0.3 dKH, and in actual use, the precision's probably no better than +/- 0.6 dKH because the actual endpoint is somewhat open to interpretation.

However, I'm aware that precision isn't the same as accuracy, so I'd like to get analyzed standards with the Hanna. It appears that Hanna's HI755-11 standard set is intended for the HI755, while they sell another standard set (the HI772-11) for the HI772 meter. Does anyone know why there would be two separate standard sets? I'm interpreting (perhaps incorrectly) that the wavelength for the two colorimeters is identical, so it's puzzling why they would supply two different calibration sets.

I should note that I have the equipment, reagents and knowledge to do my own highly accurate alkalinity titrations using a standardized HCl solution, buret, pH meter and stir plate. So one solution to the accuracy question would be to simply compare the Hanna reading to a titration of the same sample. But that's a bit inconvenient, so if anyone has thoughts about these Hanna calibration sets, I'm all ears.

If you can do your own titrations, then you can make your own inexpensive standard to keep an eye on the Hanna Alkalinity Checker. If you are very concerned about accuracy, make three standards over the range you are expecting to test and ensure your Checker is accurate and linear.

 

[Dkeller_nc]

Bear in mind that the Hanna "standards" are simply color standards, not any sort of test that evaluates the method accuracy in measuring seawater alkalinity. It's a minimal hurdle that, IMO, isn't that useful since it may convey a false sense of assurance.

Yeah, after reading a bit more about them, I see that's the case. The weird thing about it is that they provide a C of A that states the particular lot's assay results in terms of alkalinity. I guess they're useful to an extent that you can check the stability of the colorimeter, though unfortunately there's no way to set a zero and span as there is on more sophisticated instruments. It'll be interesting to compare a titration of a sample to the Hanna; I've checked the Salifert kit occasionally, and found it to be quite accurate, if somewhat imprecise.

 

[taricha]

I should note that I have the equipment, reagents and knowledge to do my own highly accurate alkalinity titrations using a standardized HCl solution, buret, pH meter and stir plate.

If that's the case then you'll be dissatisfied with the accuracy limitations of a 10mL cuvette and a color test.

I have alk kits I like just fine, but I prefer my 100mL volumetric flask, 2.5 to 3mL of .1M HCl and a pH meter.

 

[KrisReef]

I believe that the reason they have two sets of meters and two sets of calibration standards is because they wanted to avoid the confusion for people who might buy either meter and wonder if the one standard was good for both meters (which it should be). Both meters can use the same reagent too. The difference is in the units reported as the op noted.

My wife used the meter and got similar readings, repeatedly while I was on a business trip. I came home and got the same measurement. Is it accurate? I compared with my Salifert test and got the same (high) reading. I'd bumped the Dkh accidentally before I left.

 

[Dkeller_nc]

I'd bumped the Dkh accidentally before I left.

Yikes. That's the kind of stuff that keeps me up at night. I accidentally jacked my SPS tank by 1 dKH unit pretty much instantly by changing out some regenerated GFO that wasn't completely rinsed. Didn't realize it until I started to see whitened tips and faded upper surfaces on the acros a day later. Fortunately, I caught it in time, turned off the dosing pumps and did a quick WC with 7.7 dKH saltwater. 48 hours later, all is well. But I don't think that would've been the case if I'd not caught it fairly quickly.

 

[Dkeller_nc]

If that's the case then you'll be dissatisfied with the accuracy limitations of a 10mL cuvette and a color test.

I have alk kits I like just fine, but I prefer my 100mL volumetric flask, 2.5 to 3mL of .1M HCl and a pH meter.

Probably. I've a science background, and spent many years in my youth working in labs, so I've a "thing" for accuracy and precision.

My main reason for wanting the Hanna meter, though, is that I really can't leave the titration rig setup. And anything that's a PITA about testing means doing it less often. So the plan is to get something easy and quick that's hopefully accurate to within +/- 0.2 dKH and that doesn't depend on the lighting to determine the endpoint. Then back-check the quick and easy method once in a while with an accurate, large-scale titration.

One thing about KrisReef's comment. I really have to wonder about trusting an SPS tank to Neptune's upcoming Trident auto-analyzer. Neptune's been doing this stuff a long time, so I have to assume they're programming in "sanity check" limits, but I could imagine a case where the acid addition line gets clogged/pinched, and the machine thinks the tank's at 18 dKH and shuts off the doser/calc reactor. Or worse, some other error results in a tank result of 5 dKH, and the unit cranks the calc reactor to "11".

 

[KrisReef]

@Dkeller_nc

I've got a plate coral that I use as my coral indicator for tank health. It's much less accurate than any test or meter, but more reliable once you learn to read the polyp extension!
As far as my relatively new Hanna Dkh meter goes, I am very happy with it thus far. It is much faster to use than other Dkh methods and has fewer moving parts! The cuvette needs to be clean inside and out and placed in the meter the same orientation each time to get good light readings, but those things are simply procedural and easy to control for. I use Hanna for Phosphorus as well, ppb is a nice level to be working at. That meter is a bit more demanding to work with but still gives reasonable results with care.

I also just noticed that you have just joined here, so WELCOME to Reef2Reef!
I think you will like it here.

 

[Dkeller_nc]

I've used the Hanna checker 713 and 736 for years for phosphate, so I'm fairly familiar with "put the vial in at the same orientation" procedure. But it's good to hear from someone that's using one and likes it. Speed/convenience is the major objective for me - an acid titration can occasionally be done to ensure accuracy. Thanks!

 

[taricha]

I believe that the reason they have two sets of meters and two sets of calibration standards is because they wanted to avoid the confusion for people who might buy either meter and wonder if the one standard was good for both meters (which it should be). Both meters can use the same reagent too. The difference is in the units reported as the op noted.

oh, one more thing. The slightly different calibration solutions are because they are slightly different numbers. The meters and reagents are the same, just diff unit displays as others have said.
one is set to read as 5.0 dKh (89.4ppm)
and the other is set to read as 100ppm (5.59dKH)
(conversions from an online calculator)