KH Guardian(KHG) Alk calculation

[JonasRoman]

I better start posting something on R2R to begin to earn some credibility. Considering all the relevant folks are on this thread already (hello Randy, Jim and Jonas).

I've been working on alkalinity machines on and off for 10 years or so but didn't brag much about the progress. For me it became a hobby of its own and looks like 2017 is a going to be an interesting year for us all.

Now, here's what I wanted to say on the topic of pCO2/pH alkalinity method. First of all, Randy is definitely correct saying that the method is well established and feasible provided all the variables are measured well. Jim's estimates of Alk/CO2 dependency are on par with my calculations. Jonas is right saying that CO2 determination is not cheap but it does not end there. In fact it's much more than $$$ for a decent NDIR detector...

In my experience, the biggest challenge in pCO2 determination in tank water is inherent sensor drift and calibration difficulties. Last summer I have spent several months and a few $$$$ playing with everything related to CO2 and came to realization that it's virtually impossible to build a low-cost CO2 detector which can be left for years without routine calibration. While short-term measurement repeatability can be improved by using thermal stabilization, dual-beam detectors and modern front-end circuitry, the long-term heat source and detector drift and contamination need to be dealt with by other means. In my experiments with various NDIR detectors I was able to achieve 3-5 ppm accuracy and linearity in air but measurement drift was 0.5 to 2 ppm per day! This was very close to the results I was getting from my research grade Li-cor LI-6252. In other words, some sort of automatic calibration is necessary to achieve long-term stability in the field and that is the biggest challenge. Here I'm not talking about many other factors interfering with CO2 measurements such as water vapor, gas pressure and leaks and diffusion barrier fouling.

We can use buffers to calibrate pH sensors fairly reliably and virtually eliminate effects of drift. It's not so easy with CO2. We can establish zero point rather easily by scrubbing ambient air of CO2 and use it as zero gas, but we also need a second point for calibration of the slope of the sensor (span gas). They supply calibration gas mixtures in nice shiny cylinders which cost a few hundred bucks per bottle. They also make dynamic gas blenders which cost like a BMW. I ended up building one myself just to validate linearity and stability of my detectors and it was a lot of fun. By the way, the instruction manual for Li-cor recommends to perform daily calibration in order to achieve stated performance and still it costs like a Toyota.

In conclusion, while pCO2 by itself is an important subject to measure and it's quite possible to build a device for hobby use for well under $1k, the drift is an issue. Calibration with outdoor air (400ppm) once a week/month can get us to ~10-20 ppm accuracy which is acceptable for most applications, but determination of alkalinity via pCO2 demands an order of magnitude better stability and sadly we are not there yet. I wonder how's Mindstream doing over there...

Regards,
Kirill

P.S.

Jim - congrats on the deal and best of luck getting it to market! Those (Takasago?) pinch valves look awesome in star arrangement
Jonas - it's great to see yet another machine popping up! Now from Scandinavia.
Randy - thanks for your valuable input and for having us all here in your forum.

P.P.S. I'm sure you've seen it already, but here it is again. My first prototype from 9 years ago

Thanks for this very substantial information, which is very similar to my own considerations and reasons why I also abandoned all methods based on CO2(aq)-measuring. I also did the conclusion that you needs a accuracy of +- 5ppm to get reasonable results, and +- 0.02 concerning pH. I had som contacts with some companies and only the sensor should cost 1000E....The calibration issue you are telling us is very interesting information also.
I recognice your wonderful machine from some forum I think. I admire that work greatly

I wants to say that I do not see other players as concurrent´s, because as this is the product of the future there is room for more players than a few. This will be an interesting year

 

[reef_ranch]

Interesting coming year indeed! Keep up the great work guys!

 

[SCSI]

@JimWelsh - watching you making progress with your blue box was in part the reason for me to re-activate my work on the new prototype which is based on entirely different principles. As for NDIR CO2, I haven't completely disqualified it, at least not for other applications where it's entirely feasible.

@JonasRoman - I would prefer to have some healthy competition rather than none at all. Just like in sports. It would be super cool to see several machines based on different basic principles of operation to compete with each other. I'm happy to see that we already have at least two approaches implemented with pH indicator and pH electrode being used. Healthy competition leads to innovation. Next thing I would like to see is drastic reduction of the sample and reagent volume per measurement with help of microfluidic chips and such. SIA approach can be viable here as well and Jim's machine seems to employ some of that technique.

I played with SIA years ago just for fun of it. Here's one example (below) which had well over $2k in parts in it (if bought new). It had sample volume of around 0.4cc and reagent 0.1cc per measurement if I recall correctly. Teflon plunger in that syringe pump didn't like the salt crystals and started to leak in a few months...

Thanks,
Kirill

 

[JonasRoman]

I agree concerning the competion part well spoken

But I think not the sample volume is an issue because of several reasons:
1) first of all the price tag must correspond to what the machine do. This is not a space-ship and no-ones life is depending on it...we must not forget to have some realistic demands. Everything is possible, but not to costs that do not match the purpose.
2) thus, the accuracy is more important than minimize testvolume. There is nothing such a free lunch...i think it is pointless with small test-volume if you loose accuracy...then it is more reasonable to turn back to a Salifert-test
3) taking some water, maybe 2-4 litres a week from the whole system Will give you an automaticaly nice small waterchanges. The very slow and small decrease in salinity will easily be corrected with some salt in the osmosebucket.
4) Balling is rising the salinity. No one consider that an issue. This is in the same range but opposite. A small withdrawal of water Will in best case compensate for the balling-caused rising. Win Win
And as i said, despite if you have Balling or Calciumreactor, you got some nice waterchange automaticaly without doing anything but sitting in your sofa and drinking a nice cup of coffe.
So according to My opinon this is not an issue at all.

My first testperiod is now running and I measure very often 24/7(mostly 1 measure/hour). More than the average customer Will do. And still I have not paid more attention to salinitydecrease than that 10 seconds it took me to throw a few dl salt in the osmosetank at 1-2 occation.

If you wants to eliminate exactly all things you have to do manualy, I think we have forgot the purpose of this hobby a little;-)

 

[SCSI]

Well, it all really depends on the tank volumes and sample volumes. In case with KHG, they chug 50cc every time and many people would prefer to discard it. That's not insignificant if you want to run tests hourly on a smaller tank.

I agree that accuracy/repeatability is important. But I also assume that accuracy is a mandatory goal/requirement and we need to be realistic with it. I think 2-3% of reading should be acceptable.

 

[JonasRoman]

I must say that there is to be honest no indication to run a test once hourly besides researching purpose. I do not think we shall consider so frequently measuring as a realistic need at all. I made a gallup before decide som things with My machine and mostly is is sufficient measuring 4-6 times a day. Let us say that the ambitious aquarist measure 8 measures a day. That is completely enough too keep dKH extreme stable even in the most instable situation. None of these machine (incl mine) perform a continously measuring. We must be realistic and ask the maximum measure frequency that make any difference.
I did not understand at all a thread in another forum where the goal was to chase numbers in reducing water-volume to extreme small one.

The KHG so long as i understand Will pump the measured and acid water back to the system. That I agree, is not a good choice of method. They have paid a bigger price than what they get in return: lower the dKH in the aquarium to be able to measure dKH with more high frequency that is necessary...
They claim that the amount of acid is negligable. Well it as you say depending on size of aquarium.
There are always drawbacks with all submethods so the main purpose must be kept in mind when doing compromises.

Concerning precision I disagree. Let us say machine measure/calculate 2.34 meq/l..this is 6.55dKH. You add 3% wrong gives a measure of 2.34x1.03x2.8=6.75.
Already with that small error which corresponds to for example only 0.3ml too much water if measuring with 10 ml sample, give an unprecision which is worse than a Salifert-hobby-kit.
Even if you have steppers or similar with extreme precision it is always to take water from the aquarium which is sensitive. Particle in the water, with time decreased hose diameter, etc. If you already is on the edge you Will soon get innacuracy which is doing the machine not even worth half the price.

I can disclosure that my machine of these reasons Will use 50 ml each cycle and discharge this to a waste-bucket. I do not think it is wise to pump it back to the aquarium as KHG does.

It think that an aquarist Will hesitate much more of measuring an extra time because of adding acid to the aquarium, than withdrawal and as a bonus getting a healthy exchange of 50 ml water;-)

Well, I have declared My opinion and reasons of My considerations, let the customer and market decide with time.

Jonas Roman

 

[SCSI]

Peristaltic pumps are imprecise by design. Steppers may improve things a bit, but still... exact volume measurement is difficult due to pulsing effect. This error can be minimized if you increase sample volume, so I understand why some may want to use 20ml sample versus 2.0ml sample. Dealing with smaller sample volumes is inherently difficult as other factors come into play in addition to the peristaltic effects. And all these effects are cumulative. And yes, hoses tend to age and flow changes over time. Too many problems with peristaltics, dang it!

When I said that accuracy of 2-3% should be acceptable I meant long term accuracy assuming all environmental factors and interferences counted in. Month over month, not just for 2-3 days in a row. Counting temperature fluctuations, atmospheric pressure changes, filter fouling and other nasty age related things.

Ideally I want to be able to measure alkalinity continuously, just like temperature or pH. In our dreams maybe...

 

[JonasRoman]

Peristaltic pumps are imprecise by design. Steppers may improve things a bit, but still... exact volume measurement is difficult due to pulsing effect. This error can be minimized if you increase sample volume, so I understand why some may want to use 20ml sample versus 2.0ml sample. Dealing with smaller sample volumes is inherently difficult as other factors come into play in addition to the peristaltic effects. And all these effects are cumulative. And yes, hoses tend to age and flow changes over time. Too many problems with peristaltics, dang it!

When I said that accuracy of 2-3% should be acceptable I meant long term accuracy assuming all environmental factors and interferences counted in. Month over month, not just for 2-3 days in a row. Counting temperature fluctuations, atmospheric pressure changes, filter fouling and other nasty age related things.

Ideally I want to be able to measure alkalinity continuously, just like temperature or pH. In our dreams maybe...

I agree that the most beautiful solution is true continously measuring, but as long as other methods are more cheap and even more accurate there is no forces to development that part with a reasonable speed. But i admit your efforts is impressiveI have seen you machine before, and that impressed me a lot:_)

 

[Randy Holmes-Farley]

Boy, you guys sure have the troops in a frenzy of anticipation. lol

 

[nervousmonkey]

I can't wait...

https://imgflip.com/gifgenerator

 

[jerlo reef tank]

I must say that there is to be honest no indication to run a test once hourly besides researching purpose. I do not think we shall consider so frequently measuring as a realistic need at all. I made a gallup before decide som things with My machine and mostly is is sufficient measuring 4-6 times a day. Let us say that the ambitious aquarist measure 8 measures a day. That is completely enough too keep dKH extreme stable even in the most instable situation. None of these machine (incl mine) perform a continously measuring. We must be realistic and ask the maximum measure frequency that make any difference.
I did not understand at all a thread in another forum where the goal was to chase numbers in reducing water-volume to extreme small one.

The KHG so long as i understand Will pump the measured and acid water back to the system. That I agree, is not a good choice of method. They have paid a bigger price than what they get in return: lower the dKH in the aquarium to be able to measure dKH with more high frequency that is necessary...
They claim that the amount of acid is negligable. Well it as you say depending on size of aquarium.
There are always drawbacks with all submethods so the main purpose must be kept in mind when doing compromises.

Concerning precision I disagree. Let us say machine measure/calculate 2.34 meq/l..this is 6.55dKH. You add 3% wrong gives a measure of 2.34x1.03x2.8=6.75.
Already with that small error which corresponds to for example only 0.3ml too much water if measuring with 10 ml sample, give an unprecision which is worse than a Salifert-hobby-kit.
Even if you have steppers or similar with extreme precision it is always to take water from the aquarium which is sensitive. Particle in the water, with time decreased hose diameter, etc. If you already is on the edge you Will soon get innacuracy which is doing the machine not even worth half the price.

I can disclosure that my machine of these reasons Will use 50 ml each cycle and discharge this to a waste-bucket. I do not think it is wise to pump it back to the aquarium as KHG does.

It think that an aquarist Will hesitate much more of measuring an extra time because of adding acid to the aquarium, than withdrawal and as a bonus getting a healthy exchange of 50 ml water;-)

Well, I have declared My opinion and reasons of My considerations, let the customer and market decide with time.

Jonas Roman

Hi guys,
I agree with Jonas, I do not think adding acid in the aquarium even at low dose is a good thing at the aquarium. Even if the KHG has to adapt the ml of acids tested compared to the volume of the aquarium ??, otherwise there is more danger with small volumes ...
The rejection outside the tank of the tested samples is indeed a good solution to supplement the supply of NaCl. This is a very good point

 

[alanjeffery]

I like the sound of Jonas' method and approach, more of a "hobbyist" level device which is what we mostly are.
Right machine to fit the right purpose. IMO constant measuring is unnecessary, but maybe nice in the future. When Alkalinity monitoring has been tweaked and perfected, to be able so see trends throughout day and night, to further understanding and knowledge of our systems. If your Alk is changing that much, that quickly, that you "MUST" have constant monitoring/dosing you probably need to go back to the basics of reefing and not rely on sophisticated equipment so much.
How easy and how quick is it to manual titration test once a day?
And if the instructions said "After test pour sample into aquarium" Would you?

 

[JonasRoman]

This is very nice and helpful feedback for me. Thanks guys

 

[Randy Holmes-Farley]

Hi guys,
I agree with Jonas, I do not think adding acid in the aquarium even at low dose is a good thing at the aquarium. Even if the KHG has to adapt the ml of acids tested compared to the volume of the aquarium ??, otherwise there is more danger with small volumes ...
The rejection outside the tank of the tested samples is indeed a good solution to supplement the supply of NaCl. This is a very good point

While I too would dump any waste, people may be misunderstanding the term "acid". It is essentially just zero alkalinity seawater of a tiny volume and should have no noticeable impact on anything.

 

[JonasRoman]

While I too would dump any waste, people may be misunderstanding the term "acid". It is essentially just zero alkalinity seawater of a tiny volume and should have no noticeable impact on anything.

But Randy, the acid you used in the titration must at the end of the day be left in the aquarium if you dispose it into the aquarium...or?: I of course completely agree with you that the endtitrated sample has zero in alkalinity and thus at a first glance do not decrease alkalinity in the system. But the acid, amount of mmol acid that was required to get the sample to that zero alkalinity Will be released to the aquarium at last. Almost all H that the alkalinitycontributing iones took up in the titration process Will subsequently be released again when entering the aquarium. So so far as i can understand the amount of acid that is required by the titration process Will have a decreasing effect in the alkalinity in the aquarium if the samplewater is getting back in aquarium.
In big system it Will not be maybe measureable but in small system and frequent measure maybe. Why take the risk when you do not need?

 

[Randy Holmes-Farley]

But Randy, the acid you used in the titration must at the end of the day be left in the aquarium if you dispose it into the aquarium...or?: I of course completely agree with you that the endtitrated sample has zero in alkalinity and thus at a first glance do not decrease alkalinity in the system. But the acid, amount of mmol acid that was required to get the sample to that zero alkalinity Will be released to the aquarium at last. Almost all H that the alkalinitycontributing iones took up in the titration process Will subsequently be released again when entering the aquarium. So so far as i can understand the amount of acid that is required by the titration process Will have a decreasing effect in the alkalinity in the aquarium if the samplewater is getting back in aquarium.
In big system it Will not be maybe measureable but in small system and frequent measure maybe. Why take the risk when you do not need?

I agree I wouldn't add it since it is easy to collect in a jug.

That said, if you add 10 mL of exactly zero alkalinity seawater (meaning you stopped the titration at the endpoint) to a 100 gallon aquarium, the alk would drop from, say, 7.5000 dKH to 7.4998 dKH.

I just did not want folks to think one is really "adding acid". Yes, it is, but when the numbers are shown, it just doesn't seem quite so scary or risky.

 

[jerlo reef tank]

While I too would dump any waste, people may be misunderstanding the term "acid". It is essentially just zero alkalinity seawater of a tiny volume and should have no noticeable impact on anything.

Yes @Randy Holmes-Farley, thanks for the clarification that you are right to specify the small amount of acid on an average aquarium volume. What happens on small volumes ?
The variation of Kh will be greater and irregular if the doses of acids are not adapted
of the aquarium.
I think the phenomenon becomes even worse if the small volume of the system has a strong KH to go down to zero alacalinity (12dKH to 4.5 ?) What do you think guys ?
I respect the work of each person or company
Is there a mathematical relationship to go for example 12dKh to 4.5dKh with X ml of sea water to test?

 

[SCSI]

I agree I wouldn't add it since it is easy to collect in a jug.

That said, if you add 10 mL of exactly zero alkalinity seawater (meaning you stopped the titration at the endpoint) to a 100 gallon aquarium, the alk would drop from, say, 7.5000 dKH to 7.4998 dKH.

I just did not want folks to think one is really "adding acid". Yes, it is, but when the numbers are shown, it just doesn't seem quite so scary or risky.

It depends on how you *show the numbers*

For example, in our case with KHG, they mentioned 20ml sample volume. Let's assume we want to perform near continuous analysis and sample every 15 minutes on a 100G system. Using your numbers above (0.0002 dKH drop for every 10ml of fully neutralized sample), this will result in a whooping 0.27 dKH drop in 7 days if dumped back into the system. Not insignificant...

In one of my previous designs I was allowing a possibility of dumping waste back into the system, but the sample volume was 1.0 ml and I wanted to do hourly sampling.

On a side note, one would probably don't want to dump a sample spoiled by pH indicator back into the system in case if its colorimetric machine. It definitely smells toxic to me

Thanks,
Kirill

 

[JonasRoman]

I agree I wouldn't add it since it is easy to collect in a jug.

That said, if you add 10 mL of exactly zero alkalinity seawater (meaning you stopped the titration at the endpoint) to a 100 gallon aquarium, the alk would drop from, say, 7.5000 dKH to 7.4998 dKH.

I just did not want folks to think one is really "adding acid". Yes, it is, but when the numbers are shown, it just doesn't seem quite so scary or risky.

Completely agree. I calculated also on that but more on different scenario, incl worst case scenario. I realised that there would despite this be a phsycologial reluctans against putting acid back in the tank. I also thought of the aquarists with small aquarium and high measuring frecuency...: I did an example: We have an aquarium of 200 l(sorry for expression in litres;-)), and you measure 20 times a day in a week(which for sure someone will do), and we have an alkalinity around 8.5 in that tank, and the measure volume is 50ml(KHG uses 50 ml as far as I understand), then we will if we put back the sample to the aquarium decrease alkalinity in that aquarium by 0.3 dKH over a week or 0.043 each day. Now we have significant affects, and this group of aquarists also exists. I Think we cannot design a machine only for people with very big tanks and low measure frequence. That decrease the machine will of course correct by adding HCO3 after passing the low.reference value, but in long term this will lead to imbalance in Ca/KH with lower Ca. Well, I get your point and agree that in some cases it is totaly negligable, but not in all cases, and therefore I choosed the method to not put the acid back

 

[JonasRoman]

Yes @Randy Holmes-Farley, thanks for the clarification that you are right to specify the small amount of acid on an average aquarium volume. What happens on small volumes ?
The variation of Kh will be greater and irregular if the doses of acids are not adapted
of the aquarium.
I think the phenomenon becomes even worse if the small volume of the system has a strong KH to go down to zero alacalinity (12dKH to 4.5 ?) What do you think guys ?
I respect the work of each person or company
Is there a mathematical relationship to go for example 12dKh to 4.5dKh with X ml of sea water to test?

See my example above with smaller tank