Alkalinity stability? pH stability? Are they even different?

[Focustronic_Jonas]

I cannot really read the picture to tell what it is. There is no simple experiment that can distinguish bicarbonate from carbonate uptake, hence the reason it has been unclear in the scientific literature. One cannot move them independently without also changing pH. I do not know which they use, and they may use both, or they may use just one.

I'm not sure why one would want to pick between A or B. Your choice C that is better than either (both stable), and another might also be better (stable bicarbonate).

reason is that if its not worth it, its just waste of energy to chase a stable pH, (that was your main message). We are searching the truth, aren’t we, so thats why we discuss. Ofcourse pic up C is the easy way out, but then we have not answered the questions and dont know more than before.

 

[Focustronic_Jonas]

I cannot really read the picture to tell what it is. There is no simple experiment that can distinguish bicarbonate from carbonate uptake, hence the reason it has been unclear in the scientific literature. One cannot move them independently without also changing pH. I do not know which they use, and they may use both, or they may use just one.

I'm not sure why one would want to pick between A or B. Your choice C that is better than either (both stable), and another might also be better (stable bicarbonate).

Choose C is an easy way that eliminate this discussion without an answer. If its waste of time to chase pH, which this thread is about, its waste of energy and efforts going for C. So the question remains, and it has t be proven what you claim. As you say, its probably hard to in a scientific way establish if a coral takes CO3 for calcification, but if that is true, your hypothesis is not truth, and its much more important with stable alk than stable pH if you have to choose between these 2. I admit it seems hard to find articles, but some of them seems to speaks for that a coral can use CO3 aswell, and then a fluctuation of the ratio HCO3/CO3 is not a problem. Its quite logic aswell, why should a coral dont use CO3 which is the primary source for calcification ? If it uses HCO3 it must expel the H ion, but the CO3 is ”ready from start”. I think reason that literature speaks more of HCO3 as primary source is that that ion is more abundant, and its hard to distinguish them apart as they are in a sort of way same molecule, and can interconvert between in seconds. /J

 

[Randy Holmes-Farley Verified Community Expert]

reason is that if its not worth it, its just waste of energy to chase a stable pH, (that was your main message). We are searching the truth, aren’t we, so thats why we discuss. Ofcourse pic up C is the easy way out, but then we have not answered the questions and dont know more than before.

Reason for what? The only place I used the word reason in the quote you posted was referring to why it is so hard to distinguish bicarbonate from carbonate uptake in corals.

That experiment is far beyond the capability of hobbyists. It requires determining exactly which transporters are present inc roals, and selectively inhibiting them to observe the effect.

 

[Randy Holmes-Farley Verified Community Expert]

Choose C is an easy way that eliminate this discussion without an answer. If its waste of time to chase pH, which this thread is about, its waste of energy and efforts going for C. So the question remains, and it has t be proven what you claim. As you say, its probably hard to in a scientific way establish if a coral takes CO3 for calcification, but if that is true, your hypothesis is not truth, and its much more important with stable alk than stable pH if you have to choose between these 2. I admit it seems hard to find articles, but some of them seems to speaks for that a coral can use CO3 aswell, and then a fluctuation of the ratio HCO3/CO3 is not a problem. Its quite logic aswell, why should a coral dont use CO3 which is the primary source for calcification ? If it uses HCO3 it must expel the H ion, but the CO3 is ”ready from start”. I think reason that literature speaks more of HCO3 as primary source is that that ion is more abundant, and its hard to distinguish them apart as they are in a sort of way same molecule, and can interconvert between in seconds. /J

Yes, the question remains. I'm not giving an answer. That is the point of this thread: To ask and get folks thinking about answering the question.

If choice C leads to better coral health or growth than choice A and B, then it does clearly prove something.

Until there are sufficient tests of it, the answer remains unknown.

it is strangely odd to conclude that if something is hard to show one way or the other, that it must not be truth. lol

" As you say, its probably hard to in a scientific way establish if a coral takes CO3 for calcification, but if that is true, your hypothesis is not truth, and its much more important with stable alk than stable pH if you have to choose between these 2."

 

[Randy Holmes-Farley Verified Community Expert]

Its quite logic aswell, why should a coral dont use CO3 which is the primary source for calcification ? If it uses HCO3 it must expel the H ion, but the CO3 is ”ready from start”. I think reason that literature speaks more of HCO3 as primary source is that that ion is more abundant, and its hard to distinguish them apart as they are in a sort of way same molecule, and can interconvert between in seconds. /J

You may have an opinion, but seem to be missing the logic.

Corals may not use carbonate for a variety of reasons, including the fact that there is much less of it, and the fact that it may be harder to chemically transport with available proteins. No amount of wondering why they do or do not provided evidence of what they do.

The rapid interconversion says nothing about which is transported. Protein transporters are highly selective and can readily distinguish them.

 

[Hans-Werner]

Its quite logic aswell, why should a coral dont use CO3 which is the primary source for calcification ? If it uses HCO3 it must expel the H ion, but the CO3 is ”ready from start”

Maybe it is the wrong view at all.

There are anemones (which basically are corals without skeletons) with zooxanthellae that do not calcify at all, there are corals that form only spicules and there are hard corals that form a skeleton of calcium carbonate.

Maybe calcification was not the starting point but the result of a process? Maybe corals took up bicarbonate to supply CO2 to their symbionts and carbonate and calcification was just the result of this process, a kind of deposition of "waste material". In this case the calcification process is primarily a way to supply CO2 and it would not make any sense at all to take up carbonate, at least not as long as a lot of bicarbonate is available.

To my knowledge the evidence points rather to viewing calcification of hermatypic this way.

 

[arking_mark]

I have a couple practical questions here. Given the relationship between pH/Alk/CO2, if you stabilize one of these parameters, then the other two move in tandem. If you stabilize 2 of these parameters, the 3rd is as well.

If we theorize that natural CO2 levels are desirable and maybe pre-industrial even better, we would probably look to stabilize C02 between 300 - 400 .

Let's pick 350, which I believe equals about 325 matm in the ocean.

We also know that pH was around 8.2. Now I'm not sure if that 8.2 is total pH or NBS. 8.2 total is ~ 8.33 NBS. Let's split the difference and go with 8.265 NBS.

Given these 2 numbers (325 and 8.265), this would put Alk at: 6.4dKH

I'm pretty sure most people would find this Alk level too low.

If we bump pH to 8.3 nbs, then Alk would be 7.1dKH

If pH was 8.2 total (8.33 nbs) , then Alk would be 7.7dKH.

So assuming you could stabilize these parameters what would be a good target? Does one even want to have stable CO2 if it means lower Alk levels?

More interesting is many reefers keep their tanks stable at 9 dKH. For many this means a daily swing of 8.1 to 8.3. So their CO2 levels swing from 733 to 417. Is this bad?

 

[Smarkow]

I have a couple practical questions here. Given the relationship between pH/Alk/CO2, if you stabilize one of these parameters, then the other two move in tandem. If you stabilize 2 of these parameters, the 3rd is as well.

If we theorize that natural CO2 levels are desirable and maybe pre-industrial even better, we would probably look to stabilize C02 between 300 - 400 .

Let's pick 350, which I believe equals about 325 matm in the ocean.

We also know that pH was around 8.2. Now I'm not sure if that 8.2 is total pH or NBS. 8.2 total is ~ 8.33 NBS. Let's split the difference and go with 8.265 NBS.

Given these 2 numbers (325 and 8.265), this would put Alk at: 6.4dKH

I'm pretty sure most people would find this Alk level too low.

If we bump pH to 8.3 nbs, then Alk would be 7.1dKH

If pH was 8.2 total (8.33 nbs) , then Alk would be 7.7dKH.

So assuming you could stabilize these parameters what would be a good target? Does one even want to have stable CO2 if it means lower Alk levels?

More interesting is many reefers keep their tanks stable at 9 dKH. For many this means a daily swing of 8.1 to 8.3. So their CO2 levels swing from 733 to 417. Is this bad?

Curious re NBS meaning? Do you mind expounding?

My p chemistry knowledge is a bit rusty (12y out, I’m old???) but I think you are on the right track.

In physiology, buffer systems were evolved to keep pH stable so that proteins function properly within a tight range. So I think when reefers talk about alkalinity of 12 vs 7 to grow coral, but not talk about their system CO2... the meat of the concept is missed. They’re talking about the buffer of the macro-external environment, not the pH of the micro-external environment where the exposed coral tissue (protein) is. And of course nobody at the hobby level is measuring tissue pH (that I know of).

 

[arking_mark]

Curious re NBS meaning? Do you mind expounding?

My p chemistry knowledge is a bit rusty (12y out, I’m old???) but I think you are on the right track.

In physiology, buffer systems were evolved to keep pH stable so that proteins function properly within a tight range. So I think when reefers talk about alkalinity of 12 vs 7 to grow coral, but not talk about their system CO2... the meat of the concept is missed. They’re talking about the buffer of the macro-external environment, not the pH of the micro-external environment where the exposed coral tissue (protein) is. And of course nobody at the hobby level is measuring tissue pH (that I know of).

So I'm just getting into the topic as well. Basically, Total pH is the total free hydrogen ions while NBS/NIST is a measure against standardized solutions. If I understand this correctly, probes are calibrated to these standards and we measure against these. Interestingly enough, we are measuring ec across a glass which can have interference from salts and stuff. The methods used for total pH eliminates/minimizes these issues.

 

[ReefBeta]

I have a couple practical questions here. Given the relationship between pH/Alk/CO2, if you stabilize one of these parameters, then the other two move in tandem. If you stabilize 2 of these parameters, the 3rd is as well.

If we theorize that natural CO2 levels are desirable and maybe pre-industrial even better, we would probably look to stabilize C02 between 300 - 400 .

Let's pick 350, which I believe equals about 325 matm in the ocean.

We also know that pH was around 8.2. Now I'm not sure if that 8.2 is total pH or NBS. 8.2 total is ~ 8.33 NBS. Let's split the difference and go with 8.265 NBS.

Given these 2 numbers (325 and 8.265), this would put Alk at: 6.4dKH

I'm pretty sure most people would find this Alk level too low.

If we bump pH to 8.3 nbs, then Alk would be 7.1dKH

If pH was 8.2 total (8.33 nbs) , then Alk would be 7.7dKH.

So assuming you could stabilize these parameters what would be a good target? Does one even want to have stable CO2 if it means lower Alk levels?

More interesting is many reefers keep their tanks stable at 9 dKH. For many this means a daily swing of 8.1 to 8.3. So their CO2 levels swing from 733 to 417. Is this bad?

You need to stablized the CO2 dissolved in water, not in surrounding air. So according the the table earlier, it's alk 8 dkh, pH 8.30, CO2 0.0207.

 

[ReefBeta]

@Randy Holmes-Farley I'm trying to put together a spreadsheet of this calculation. I'm looking at these equations. But I'm not sure if I got the right K1 and K2. The value I found are K1 = 4.25E-07, K2 = 4.80E-11. Are those correct? With those number the result are off from your table.

With those two values, the table I got is

pH	CO2	HCO3	CO3
7.6	0.446	7.540	0.014
7.65	0.400	7.584	0.016
7.7	0.358	7.624	0.018
7.75	0.320	7.659	0.021
7.8	0.287	7.690	0.023
7.85	0.256	7.717	0.026
7.9	0.229	7.741	0.030
7.95	0.205	7.762	0.033
8	0.183	7.780	0.037
8.05	0.163	7.795	0.042
8.1	0.146	7.807	0.047
8.15	0.130	7.817	0.053
8.2	0.116	7.824	0.060
8.25	0.104	7.830	0.067
8.3	0.092	7.833	0.075
8.35	0.082	7.833	0.084
8.4	0.073	7.832	0.094
8.45	0.065	7.829	0.106
8.5	0.058	7.823	0.119
8.55	0.052	7.815	0.133
8.6	0.046	7.805	0.149

I tried to plot them and got this

It looks the same shape as that on wiki, but the center point is shifted to pass 8. Are K1 and K2 constants, or they depend on something?

 

[arking_mark]

@Randy Holmes-Farley I'm trying to put together a spreadsheet of this calculation. I'm looking at these equations. But I'm not sure if I got the right K1 and K2. The value I found are K1 = 4.25E-07, K2 = 4.80E-11. Are those correct? With those number the result are off from your table.

With those two values, the table I got is

pH	CO2	HCO3	CO3
7.6	0.446	7.540	0.014
7.65	0.400	7.584	0.016
7.7	0.358	7.624	0.018
7.75	0.320	7.659	0.021
7.8	0.287	7.690	0.023
7.85	0.256	7.717	0.026
7.9	0.229	7.741	0.030
7.95	0.205	7.762	0.033
8	0.183	7.780	0.037
8.05	0.163	7.795	0.042
8.1	0.146	7.807	0.047
8.15	0.130	7.817	0.053
8.2	0.116	7.824	0.060
8.25	0.104	7.830	0.067
8.3	0.092	7.833	0.075
8.35	0.082	7.833	0.084
8.4	0.073	7.832	0.094
8.45	0.065	7.829	0.106
8.5	0.058	7.823	0.119
8.55	0.052	7.815	0.133
8.6	0.046	7.805	0.149

I tried to plot them and got this

It looks the same shape as that on wiki, but the center point is shifted to pass 8. Are K1 and K2 constants, or they depend on something?

This thread might help...

Equation for graphing Alk vs pH for a given CO2 level

@Randy Holmes-Farley Could you share the equation(s) used for making this graph?

www.reef2reef.com

 

[ReefBeta]

This thread might help...

Equation for graphing Alk vs pH for a given CO2 level

@Randy Holmes-Farley Could you share the equation(s) used for making this graph?

www.reef2reef.com

Cool. The formula in linked paper is the same as wiki. Still didn't mention what K1, K2 should be, or maybe I don't understand what it's saying.

But I found this one. In Table 1 listed some measurements from previous works. I took the Roy et al. (1993) one, pK1 = 5.85, pK2 = 8.92. The result came out a bit different from Randy's, but a lot closer.

pH	CO2	HCO3	CO3
7.60	0.133	7.507	0.359
7.65	0.119	7.480	0.402
7.70	0.105	7.446	0.449
7.75	0.093	7.406	0.501
7.80	0.083	7.359	0.558
7.85	0.073	7.305	0.622
7.90	0.065	7.244	0.692
7.95	0.057	7.174	0.769
8.00	0.050	7.097	0.853
8.05	0.044	7.010	0.946
8.10	0.039	6.915	1.047
8.15	0.034	6.809	1.156
8.20	0.030	6.694	1.276
8.25	0.026	6.569	1.405
8.30	0.023	6.434	1.543
8.35	0.020	6.288	1.692
8.40	0.017	6.131	1.852
8.45	0.015	5.964	2.021
8.50	0.013	5.787	2.200
8.55	0.011	5.600	2.389
8.60	0.010	5.404	2.586

If to stablize bicarbonate to 6 dKH, it gets

pH	CO2	ALK	CO3
7.60	0.107	6.394	0.287
7.65	0.095	6.417	0.322
7.70	0.085	6.446	0.362
7.75	0.076	6.481	0.406
7.80	0.067	6.522	0.455
7.85	0.060	6.571	0.511
7.90	0.053	6.626	0.573
7.95	0.048	6.691	0.643
8.00	0.042	6.764	0.721
8.05	0.038	6.847	0.809
8.10	0.034	6.942	0.908
8.15	0.030	7.049	1.019
8.20	0.027	7.170	1.143
8.25	0.024	7.307	1.283
8.30	0.021	7.461	1.439
8.35	0.019	7.634	1.615
8.40	0.017	7.829	1.812
8.45	0.015	8.048	2.033
8.50	0.013	8.295	2.281
8.55	0.012	8.571	2.559
8.60	0.011	8.882	2.872

My tank recently running pH from 8.2 to 8.5. So to have stable bicarbonate, the total alkalinity will be from 7.17 at night, to 8.295 at peak. I don't know where this is going ...

Anyway, I plotted the pass 3 months data from Alkatronic for pH, ALK, HCO3.

HCO3 swing more than ALK, mostly 0.2~0.5 more. But the difference from ALK puts more impact on HCO3 than pH. So if ALK if flatlined, the HCO3 will look more like the pH trend, which is not bad, I think.

 

[arking_mark]

Cool. The formula in linked paper is the same as wiki. Still didn't mention what K1, K2 should be, or maybe I don't understand what it's saying.

But I found this one. In Table 1 listed some measurements from previous works. I took the Roy et al. (1993) one, pK1 = 5.85, pK2 = 8.92. The result came out a bit different from Randy's, but a lot closer.

pH	CO2	HCO3	CO3
7.60	0.133	7.507	0.359
7.65	0.119	7.480	0.402
7.70	0.105	7.446	0.449
7.75	0.093	7.406	0.501
7.80	0.083	7.359	0.558
7.85	0.073	7.305	0.622
7.90	0.065	7.244	0.692
7.95	0.057	7.174	0.769
8.00	0.050	7.097	0.853
8.05	0.044	7.010	0.946
8.10	0.039	6.915	1.047
8.15	0.034	6.809	1.156
8.20	0.030	6.694	1.276
8.25	0.026	6.569	1.405
8.30	0.023	6.434	1.543
8.35	0.020	6.288	1.692
8.40	0.017	6.131	1.852
8.45	0.015	5.964	2.021
8.50	0.013	5.787	2.200
8.55	0.011	5.600	2.389
8.60	0.010	5.404	2.586

If to stablize bicarbonate to 6 dKH, it gets

pH	CO2	ALK	CO3
7.60	0.107	6.394	0.287
7.65	0.095	6.417	0.322
7.70	0.085	6.446	0.362
7.75	0.076	6.481	0.406
7.80	0.067	6.522	0.455
7.85	0.060	6.571	0.511
7.90	0.053	6.626	0.573
7.95	0.048	6.691	0.643
8.00	0.042	6.764	0.721
8.05	0.038	6.847	0.809
8.10	0.034	6.942	0.908
8.15	0.030	7.049	1.019
8.20	0.027	7.170	1.143
8.25	0.024	7.307	1.283
8.30	0.021	7.461	1.439
8.35	0.019	7.634	1.615
8.40	0.017	7.829	1.812
8.45	0.015	8.048	2.033
8.50	0.013	8.295	2.281
8.55	0.012	8.571	2.559
8.60	0.011	8.882	2.872

My tank recently running pH from 8.2 to 8.5. So to have stable bicarbonate, the total alkalinity will be from 7.17 at night, to 8.295 at peak. I don't know where this is going ...

Anyway, I plotted the pass 3 months data from Alkatronic for pH, ALK, HCO3.

HCO3 swing more than ALK, mostly 0.2~0.5 more. But the difference from ALK puts more impact on HCO3 than pH. So if ALK if flatlined, the HCO3 will look more like the pH trend, which is not bad, I think.

Great analysis...but what are you trying to find? What question are you trying to answer?

 

[ReefBeta]

Great analysis...but what are you trying to find? What question are you trying to answer?

I'm going along the way with Randy's thought on stablizing bicarbonate. But I'm not sure where I'm going honestly ...

 

[arking_mark]

I'm going along the way with Randy's thought on stablizing bicarbonate. But I'm not sure where I'm going honestly ...

@Randy Holmes-Farley I hope these numbers are correct...I don't think they match your #s, so I'm guessing they are off somewhere.

So if you fix pH at 8.3, and swing Alk from say 7.5 to 8.5.

Tank measured Alk = 7.5 dKH ( 2700.0 )
Tank measured pH = 8.3 NBS
Calculated Results:
Alk = 7.499999999999999 dKH
pH = 8.163015775492143 Total
CO2 = 344 Dry mole fraction of CO2
CO3out = [308.68319422]
HCO3out = [1956.92406063]
CO3 % = [13.62474425]

Tank measured Alk = 8.5 dKH ( 3060.0 )
Tank measured pH = 8.3 NBS
Calculated Results:
Alk = 8.5 dKH
pH = 8.163015775492141 Total
CO2 = 393 Dry mole fraction of CO2
CO3out = [351.85079793]
HCO3out = [2230.58885322]
CO3 % = [13.62474425]

I see a HCO3 upswing of 14%

If we fix Alk at 7.5 and swing pH from 8.1 to 8.2.

Tank measured Alk = 7.5 dKH ( 2700.0 )
Tank measured pH = 8.1 NBS
Calculated Results:
Alk = 7.499999999999999 dKH
pH = 7.963015775492142 Total
CO2 = 608 Dry mole fraction of CO2
CO3out = [216.81877016]
HCO3out = [2178.50150367]
CO3 % = [9.05176533]

Tank measured Alk = 7.5 dKH ( 2700.0 )
Tank measured pH = 8.2 NBS
Calculated Results:
Alk = 7.499999999999999 dKH
pH = 8.063015775492142 Total
CO2 = 460 Dry mole fraction of CO2
CO3out = [259.94289991]
HCO3out = [2074.62184692]
CO3 % = [11.13453376]

I see a HCO3 downswing of 4.7%.

If pH swings from 8.0 to 8.3, then...

Tank measured Alk = 7.5 dKH ( 2700.0 )
Tank measured pH = 8.0 NBS
Calculated Results:
Alk = 7.499999999999999 dKH
pH = 7.863015775492142 Total
CO2 = 797 Dry mole fraction of CO2
CO3out = [179.34775013]
HCO3out = [2268.59473737]
CO3 % = [7.32646911]

Tank measured Alk = 7.5 dKH ( 2700.0 )
Tank measured pH = 8.3 NBS
Calculated Results:
Alk = 7.499999999999999 dKH
pH = 8.163015775492143 Total
CO2 = 344 Dry mole fraction of CO2
CO3out = [308.68319422]
HCO3out = [1956.92406063]
CO3 % = [13.62474425]

I see a HCO3 downswing of 14%.

Maybe I'm not doing this right, but , 7.5 to 8.5 dKH swing at a fixed 8.3pH seems to be the same as a 8.0 to 8.3 pH swing at a fixed 7.5 dKH with respect to HCO3, accept they move in different directions.

 

[Randy Holmes-Farley Verified Community Expert]

We've discussed on other threads the complexities of these equations since there are a number of different pH scales used in seawater.. The pH scale chosen will shift the curves around a bit, but not change the shape.

 

[Doreno]

How much ph value changes in a real ocean / marine reef lagoon during the day?

 

[Cory]

How much ph value changes in a real ocean / marine reef lagoon during the day?

It can vary from 8.6 down to 7.8 based on location. Lagoons get the big ph shifts, deep water gets the the low ones.

 

[Doreno]

It can vary from 8.6 down to 7.8 based on location. Lagoons get the big ph shifts, deep water gets the the low ones.

I asked about this because if in natural reef as you said ph changes from 7,8 to 8,6 during the day , why we should worry about changes 7,9 to 8,3 in our tanks…