KH Guardian: Automatic Alkalinity Controller- My Experiences

[Jonty]

yeah I have had most of my changes in 0.1 increments.

I wonder if you need to adjust your current dosing amount (if its dropping quickly), up your test frequency or adjust your tank size/max adjustment amount in the settings?

I have adjusted tank size and will monitor over next 24 hrs.

 

[Jonty]

I did just forget the Dastaco unit has a light sensor so it doses more in the day than night to compensate for daytime ALK take up and smooth the highs and lows this may explain some of the jumps as well, to be clear we are only talking about a short term 0.1 rise above set point but it is fun to try to see how flat you can make the plot line :)

 

[Jonty]

I believe how accurately you mix the reagent will impact the reading and necessitate an adjustment for the duration of the reagent use. I do not know if this effects you but it is worth considering.

 

[Carlos@CoralVue]

I believe how accurately you mix the reagent will impact the reading and necessitate an adjustment for the duration of the reagent use. I do not know if this effects you but it is worth considering.

Yes, correct. Sometimes if the KHG is off there is a chance that the reagent was not mixed correctly and it is not the right concentration.

 

[samparker]

Scale was used to measure out the 1500 ml. Same scale that was used to measure the 500ml for both of the dKh standard solutions

1500 grams you mean? Manual states:

"Factory supplied KHG reagent solution are concentrated. To achieve the best accuracy, users must proper dilute it. You should use 1500 grams of RODI water for dilution. Please note the unit of RODI water is grams, not mililiter. Please use a electronic scale to weigh 1500 grams of water at room temperature, and keep the error to within 0.1 grams. Each new dilution of the KHG reagents is enough for approximately 2 month, based on 4 hours test interval and about 4 grams of reagent consumed per test."

 

[Jonty]

1gram=1ml H2O

Sure but can you measure .1 ml?

 

[Rick.45cal]

@Sps3Sixty have you run anymore tests?

 

[CoralFragZ]

Thanks for Sharing. What is the overall impression for the owners?

 

[Rick.45cal]

I love mine :)

 

[Jonty]

I have no regrets a great bit of kit.

 

[CoralFragZ]

what is your error correction? I made up 10dkh standard and my hanna checks that at 9.85. Hanna checks my tank at 8.65 however the unit on test 7 is at 8DKH. The settings shows an error of .5 should I bump that up to 1.1 to get it to 8.6?

 

[CoralFragZ]

Answered.

 

[Rick.45cal]

I didn't introduce an error correction into mine.

 

[Jonty]

I found mine to be very close to my Hanna checker I did not need to enter a correction factor.

 

[Carlos@CoralVue]

what is your error correction? I made up 10dkh standard and my hanna checks that at 9.85. Hanna checks my tank at 8.65 however the unit on test 7 is at 8DKH. The settings shows an error of .5 should I bump that up to 1.1 to get it to 8.6?

Based on the experience from other people here, I would double check the reading from the optical device against a test kit like Salifert. I know if you read the beginning of this thread you will find that some people's optical devices were off.

Also, have you made the calibration adjustment on the unit itself so it reads the correct dKH?

The reason why the calibration adjustment was added to the unit is to compensate for the variations on the pH probe readings as well as any small differences in the reagent concentration when mixed.

If the unit is being precise (meaning constantly giving you the same reading) but it's accuracy is off, then you will need to make the adjustment under the system setup to calibrate the unit itself to give you the correct reading you need. After that, the unit should be accurate and precise until you either change the probe or replenish your reagent solution. Then you may have to do another calibration adjustment.

 

[Randy Holmes-Farley Verified Community Expert]

I did just forget the Dastaco unit has a light sensor so it doses more in the day than night to compensate for daytime ALK take up and smooth the highs and lows this may explain some of the jumps as well, to be clear we are only talking about a short term 0.1 rise above set point but it is fun to try to see how flat you can make the plot line :)

Interestingly, I'm not sure getting the measured value of alkalinity by this method to be flat actually results in the lowest change in true alkalinity from day to night.

In detail, the endpoint of a pH titration to determine total alkalinity changes as the CO2 level in the water changes. When there is more CO2 in the water (i.e., the starting pH is lower), the proper pH titration endpoint is also lower.

So at night when there is more CO2 in most reef tanks, you may not be getting an accurate alkalinity reading. It might read the same alkalinity as during the day, but actually be higher at night than the machine stated because it didn't titrate down to the actual endpoint for that amount of CO2.

The effect is likely not big enough to be any real concern, but for folks trying to flatten the alk changes as much as possible for whatever reason, it may be.

 

[Randy Holmes-Farley Verified Community Expert]

what is your error correction? I made up 10dkh standard and my hanna checks that at 9.85. Hanna checks my tank at 8.65 however the unit on test 7 is at 8DKH. The settings shows an error of .5 should I bump that up to 1.1 to get it to 8.6?

How did you make that standard?

 

[Rick.45cal]

I've nearly got my dosing dialed in and it seems to stay pretty stable, I've got my set point at 7.5dkh and my tank seems to have settled around 7.6-7.7 dKH.

It took a little time but I figured out that the less you mess with your dosing the better. It has definitely help me stabilize my alkalinity. There now is growth more like what I expected. I have no doubt my alkalinity was as low as the KHG told me in the beginning. I'm more than happy with the results it has already given me, the KHG is a good fit for my tank. :)

 

[Carlos@CoralVue]

I would suggest using a Salifert kit instead of the optical one.

http://wamas.org/forums/topic/41663-diy-10-dkh-alkalinity-standard/
500g rodi, 7.5g baking soda
then using 10g of that solution mixed with 490g rodi
Tested with the Hanna to verify. The one I mixed up came back 183ppm or 10.248dKH.
Within the 5% error, but 5% of the measurement is 9.15ppm or .51 dkh




I ran just the 10dKH standard on the Guardian after I purged the sw line and the chamber and it ran 8 tests before running out of standard
1-8.00
2-8.00
3-8.00
before the 4th test I changed the KH auto correction to 8, was previously set at 6.5 from running on tank. and had gotten
KH > ERR for test 1-3. I also got KH>ERR on test 4. I went back and manually changed the last test number to 8.0. I think that sometimes it doesn't update this if there is Any error during the test. even though KH is most likely due to being greater than 1.5 from the auto correction number.
4- 9.00
5-9.20
6-9.20
7-9.40
8-9.40

So I placed Guardian back on tank and let it run every 30 min for 7 hours. Giving me a range 6.60-6.70. This morning I +1.4 ADJ KH.
Which brought it up to 8.00 the same numbers I am getting with Hanna 142/143ppm 7.952 &8.008dKH. Lights are off during the day I am going to continue to allow Guardian to run every 30 minutes. I will come back and test with Hanna every couple hours to verify the numbers. I would expect the numbers to climb since whole system in on reverse cycle. Running 60ml /min from masterflex pump on Reef Octopus CR5000D reactor set at 6.60 pH.

 

[Randy Holmes-Farley Verified Community Expert]

500g rodi, 7.5g baking soda
then using 10g of that solution mixed with 490g rodi
Tested with the Hanna to verify. The one I mixed up came back 183ppm or 10.248dKH.
.

That won't be perfectly accurate in a titration, and of unknown accuracy (to me) with the Hanna.

The reason I asked is because the pH endpoint of a total alkalinity titration is different in fresh and seawater because the acidity of bicarbonate is different between the two settings.

In a solution of sodium bicarbonate (baking soda) in RO/DI made to 1 meq/L (2.8 dKH), the pH endpoint is about pH 4.67 (calculated on page 182 of Aquatic Chemistry Concepts by James Pankow). The solution you made will have an endpoint of about pH 4.4 since it has higher alkalinity.

Seawater with an alkalinity of 10 dKH and 25 deg C will have a pH endpoint of about 4.14.

Thus the "standard" 10 dKH will read somewhat higher in alkalinity than the reading you'd get in 10 dKH seawater because not enough acid has been added to get to the actual endpoint in seawater (or too much as was added in freshwater, depending on which endpoint the device chooses to use). Exactly how much this pH endpoint difference makes in the total alk determination depends on the slope of the acid vs pH line at the endpoint, and it is pretty steep so the error is smallish.

In this thread on the accuracy of this device, I show data from my testing where an inaccuracy of 0.7 pH units made a 7% uncertainty in the result. Interpolating, an "uncertainty" of 0.25 pH units (by using the wrong endpoint) will cause an error of 2.5%, or 0.25 dKH out of 10 dKH.

https://www.reef2reef.com/threads/kh-guardian-khg-alk-calculation.277092/#post-3362058

This I conclude that your "standard" is off by 2.5% or 0.25 dKH due to the method of determination of total alkalinity being imperfect for freshwater if it is perfectly designed for seawater.