Hanna alk testing off by 0.8 dKh on one tank

[Sdbuehler1]

Last week I got an Apex Trident for my 100 gallon mixed reef tank. After letting it run tests for several days and then doing a calibration it is reading the following as of this morning:

Alk 7.48 dKh (hanna 8.3 dKH)
Calcium 403 ppm (hanna 413)
Magnesium 1360 ppm (salifert 1350)

As you can see above the calcium and magnesium are pretty close to my manual testing but the difference in alkalinity is pretty big ( 0.8 dKH ). I decided to get a salifert alkalinity test and it measured 7.5 dKH which pretty much matches what the Trident reads. So now this leaves me to believe that the hanna tester is off and frankly I am not surprised as I have had batches where the testing jumps up or down 0.5 dKH after switching to a new bottle. I am fine with accepting that the hanna tester is probably inaccurate, but here is the weird part...

In my 20 gallon tank the hanna reads 9.1 and the salifert reads 8.9 so its only only a difference of 0.2 but in my 100 gallon tank, the hanna reads 8.3 and the salifert reads 7.5. Any ideas on why the reading would be way off in just one tank and not the other? I am not a chemist but It makes me think that the hanna reagent is reacting to something in my 100 gallon tank that is throwing it off.

 

[Formulator]

Last week I got an Apex Trident for my 100 gallon mixed reef tank. After letting it run tests for several days and then doing a calibration it is reading the following as of this morning:

Alk 7.48 dKh (hanna 8.3 dKH)
Calcium 403 ppm (hanna 413)
Magnesium 1360 ppm (salifert 1350)

As you can see above the calcium and magnesium are pretty close to my manual testing but the difference in alkalinity is pretty big ( 0.8 dKH ). I decided to get a salifert alkalinity test and it measured 7.5 dKH which pretty much matches what the Trident reads. So now this leaves me to believe that the hanna tester is off and frankly I am not surprised as I have had batches where the testing jumps up or down 0.5 dKH after switching to a new bottle. I am fine with accepting that the hanna tester is probably inaccurate, but here is the weird part...

In my 20 gallon tank the hanna reads 9.1 and the salifert reads 8.9 so its only only a difference of 0.2 but in my 100 gallon tank, the hanna reads 8.3 and the salifert reads 7.5. Any ideas on why the reading would be way off in just one tank and not the other? I am not a chemist but It makes me think that the hanna reagent is reacting to something in my 100 gallon tank that is throwing it off.

I think its more about test variability. The salifert test has more inherent variability since it relies on your eyes to match a color change. The hanna test and salifert test use essentially the same same chemistry (bromophenol blue indicator), but one uses a colorimeter and one relies on your eyes.

Regarding the trident, you will drive yourself crazy trying to get it perfectly aligned with your manual test results. You can get really close by calibrating against your manually tested tank water, but then its better to use the trident for monitoring trends and keeping stability rather than chasing perfect alignment between tests. So if you want to switch to trident exclusively, just take the value you get as your baseline target and strive to keep that steady. Whether your true alkalinity is 8.7 or 9.1 is less important than stability at either value.

 

[Sdbuehler1]

I think its more about test variability. The salifert test has more inherent variability since it relies on your eyes to match a color change. The hanna test and salifert test use essentially the same same chemistry (bromophenol blue indicator), but one uses a colorimeter and one relies on your eyes.

Regarding the trident, you will drive yourself crazy trying to get it perfectly aligned with your manual test results. You can get really close by calibrating against your manually tested tank water, but then its better to use the trident for monitoring trends and keeping stability rather than chasing perfect alignment between tests. So if you want to switch to trident exclusively, just take the value you get as your baseline target and strive to keep that steady. Whether your true alkalinity is 8.7 or 9.1 is less important than stability at either value.

I think I have already driven myself crazy lol but I definitely think the hanna alk reagent is the consistent of the bunch. I use hanna for alk, calcium, phosphate, and nitrate and the alk is the one test where the reagents are all over the place from batch to batch. Thanks for chiming in, I'm going to let the trident run for another week and then experiment with it controlling my DOS for alk and calcium.

 

[Formulator]

FWIW, I switched to trident controlled dosing “cold turkey” back in the spring and haven’t looked back. Stability is better than I’ve ever achieved in my 9 years in the hobby and my corals show it. I would go for it. You wont regret it!

 

[Sdbuehler1]

FWIW, I switched to trident controlled dosing “cold turkey” back in the spring and haven’t looked back. Stability is better than I’ve ever achieved in my 9 years in the hobby and my corals show it. I would go for it. You wont regret it!

That's awesome to hear, I hope to have the same experience.

 

[Sphyrna_gal]

That's awesome to hear, I hope to have the same experience.

I've had the same exp with the ALK Hanna tester and I am also just thinking of switching to trident. Looking forward to seeing how your tank progresses after the switch