KH Director discrepancy

mwilk19 · Jun 28, 2019

My KH Director is showing a reading of 8.0 DKH. My Hanna checker shows 8.8 DKH and Salifert at 8.6. That's a pretty wide range. I have recently calibrated the probe in the KH Director so that shouldn't be the reason.

Water Dog · Jun 28, 2019

Apparently the Neptune Apex guys are experiencing the same thing with their Hanna Alk checkers, getting anywhere between 0.7 to 1 dkh higher results than what their Tridents are reading for Alk. As far as the Salifert results go, I haven’t seen any comparisons as yet. The question is, which one are we to trust as being accurate?

mwilk19 · Jun 28, 2019

Water Dog said:
Apparently the Neptune Apex guys are experiencing the same thing with their Hanna Alk checkers, getting anywhere between 0.7 to 1 dkh higher results than what their Tridents are reading for Alk. As far as the Salifert results go, I haven’t seen any comparisons as yet. The question is, which one are we to trust as being accurate?

That's the problem. I know we're looking for trends as much as anything but a 10% difference in readings is pretty significant.

Water Dog · Jun 28, 2019

mwilk19 said:
That's the problem. I know we're looking for trends as much as anything but a 10% difference in readings is pretty significant.

Indeed that is quite a discrepancy. However, if your corals are doing fine and are healthy, I would be hesitant to make any changes to your Alk level.

mwilk19 · Jun 28, 2019

Water Dog said:
Indeed that is quite a discrepancy. However, if your corals are doing fine and are healthy, I would be hesitant to make any changes to your Alk level.

I just went through an alkalinity spike that killed a couple of my colonies and damaged a few more. I'm just trying to determine where my alkalinity really is and try to use the KH director to stabilize it.

Water Dog · Jun 28, 2019

mwilk19 said:
I just went through an alkalinity spike that killed a couple of my colonies and damaged a few more. I'm just trying to determine where my alkalinity really is and try to use the KH director to stabilize it.

Then you will be well served by your KH Director. There is no question that it’s automatic testing will be more precise than manual testing. Thus, it will be able to accurately detect swings regardless of whether the true Alk reading is at 8.0 or 8.8.

Kyl · Jun 28, 2019

Unless you're using the Hanna alkalinity calibration standards to make sure the checker is in range, there is no way to know for sure.

Leadfooted · Jun 28, 2019

mwilk19 said:
I just went through an alkalinity spike that killed a couple of my colonies and damaged a few more. I'm just trying to determine where my alkalinity really is and try to use the KH director to stabilize it.

Where was your PH level when your alk spiked?

mwilk19 · Jun 28, 2019

Leadfooted said:
Where was your PH level when your alk spiked?

My PH varies from about 7.85 at night to a little over 8 during the day.

Leadfooted · Jun 28, 2019

mwilk19 said:
My PH varies from about 7.85 at night to a little over 8 during the day.

I was just curious because I read recently high 8.3+ PH can cause the ALK spikes so I was curious if that happened to you.

jschultzbass · Jun 28, 2019

GHL makes a 7.5 KH standard solution. I picked that up to make sure my testing was accurate. I have the same issue as you and my Director is not even close to accurate. I'm working with GHL through their online support system but so far I am very unimpressed. My Hannah, Salifert, Red Sea, and Tropic Marin KH test kits all come within reason of the 7.5 standard (+/- 2 to 3) But the Director reads 6.4.

kodo28 · Jun 28, 2019

I do use also the 7.5 KH standard solution and I get reading with 0.2dkh max difference with the solution and 0.3dkh difference with the Hanna.
Using a precision scale for all calibrations and also using it when testing with the Hanna checker.

smartwater101 · Jun 29, 2019

Leadfooted said:
I was just curious because I read recently high 8.3+ PH can cause the ALK spikes so I was curious if that happened to you.

High pH will cause an alk DROP, not spike. Absorption is increased with higher pH, its what many people do to increase coral growth.

Leadfooted · Jun 29, 2019

smartwater101 said:
High pH will cause an alk DROP, not spike. Absorption is increased with higher pH, its what many people do to increase coral growth.

Thank you, I got that mixed up.

Brew12 · Jun 29, 2019

I have the GHL reference solution and find my KH director and Hanna checker to be within 0.2dkh of it. Accurate calibration of dosing heads 1 and 2 is critical to get an accurate measurement. Even a tiny amount of air in the reagent line will also cause issues.

Mine KH director wasn't very accurate for the first few samples but it kept getting better over the course of a week and now I trust it completely.

As an aside, the Hanna alk reagent has a very finite shelf life. If it's been open for more than 2 months I wouldn't trust its accuracy completely.

Gonzo74 · Sep 6, 2019

jschultzbass said:
GHL makes a 7.5 KH standard solution. I picked that up to make sure my testing was accurate. I have the same issue as you and my Director is not even close to accurate. I'm working with GHL through their online support system but so far I am very unimpressed. My Hannah, Salifert, Red Sea, and Tropic Marin KH test kits all come within reason of the 7.5 standard (+/- 2 to 3) But the Director reads 6.4.

I’m having the same issue with my KH Director.

Kyl · Sep 6, 2019

Calibrate the reagent head at least again, and include the tenths of a ML in that. It does require a fine graduated cylinder, or a scale with low enough weight resolution. There is quite a big difference from rounding that figure up or down, or eyeballing it if there are no graduations between 4 and 5 ml. Something I found out and corrected, and now the kHD reads within .2 of the 7.5 reference solution with a 80ml sample being used.

jschultzbass · Sep 6, 2019

Kyl said:
Calibrate the reagent head at least again, and include the tenths of a ML in that. It does require a fine graduated cylinder, or a scale with low enough weight resolution. There is quite a big difference from rounding that figure up or down, or eyeballing it if there are no graduations between 4 and 5 ml. Something I found out and corrected, and now the kHD reads within .2 of the 7.5 reference solution with a 80ml sample being used.

What are you using to measure for calibration?

Kyl · Sep 6, 2019

A 5ml graduated cylinder, broken into tenths.

csb123 · Sep 6, 2019

Brew12 said:
As an aside, the Hanna alk reagent has a very finite shelf life. If it's been open for more than 2 months I wouldn't trust its accuracy completely.

Has anyone else noticed this? I’ve noticed slight differences between bottles of the reagent. As a result I’ve been mixing 6 bottles at a time (for me a six month supply,) and keeping it in black bottle. This has given me more stable results.