Alkalinity stability? pH stability? Are they even different?

[thermoJoe]

Nice thread. Recently I installed a Trident to monitor the "big three" (ha, trident, took me a bit to get the name). I was surprise at just how much I was driving diel Alk changes by adding ATO with kalkwasser only if the pH dropped below 8.1 or so (I was trying to keep 8 < pH < 8.3). The fluctuations in Alk were so large (~0.8 dKH) that it started causing some problems with the Trident, as I noticed on several occasions that the Trident took double samples. Turns out, if a current measurement differs too much from the previous one, then the Trident considers it in error and will resample. Big fluctuations in Alk will caused the issue. Anyway, I stopped constraining the ATO+kalkwasser additions to control pH, and I increased my Alk operating conditions (I was running closer to 2.3-2.5 mEq/L (6.5-7 dKH) that is in natural seawater, but now run closer to 8.5 dKH). The definition of alkalinity is it buffering capacity, so higher Alk will result in lower pH swings.

I also got briefly interested in natural fluctuation observed in Alk and pH, and found this article, which relates to this thread, but it is for microcosm systems https://peerj.com/articles/378/ but it may be of interest to some here.

 

[rishma]

RHF - on behalf of the reefing community, thank you once again for making water chemistry accessible and understandable.

 

[User1]

I was trying to smooth out my Alk consumption over 24 hours but didn't pay attention to ph. Didn't even think about it. I was going to ask how Mother Nature handles this or if it has ever been tested. Those with automation tools checking both Alk and ph it would be interesting to see how they compare.

I'm not sure I could due to the peaks occurring at different times of the day. Typically pattern below.

 

[elysics]

I was trying to smooth out my Alk consumption over 24 hours but didn't pay attention to ph. Didn't even think about it. I was going to ask how Mother Nature handles this or if it has ever been tested. Those with automation tools checking both Alk and ph it would be interesting to see how they compare.

I'm not sure I could due to the peaks occurring at different times of the day. Typically pattern below.

You reached those PH ranges without thinking about PH? Did you combine all PH raising methods together by accident? I'm jealous.

 

[Lasse]

In some way corals/photosynthesis is taking up H+ during the day....

No - they are not taking up hydrogen ions at all IMO - the zooxanthellae in the coral (and other algae) takes up more CO2 gas from the water compared with what is produced of all cell metabolism and transport in the air/water interface (in an aquarium) . The extra hydrogen ions (or more in a scientist way today hydronium) that will show up when CO2 gas is taken away from water comes from the the equilibrium equation of the carbonate system in water.

CO2<=>H2CO3 <=> HCO3 <=> CO3.

And to make more difficult - there is also an equilibrium equation according to CO2 in air and water there the CO2 concentration in water is mostly depended of air concentration. CO2 air <=> CO2 water. More CO2 in air - more CO2 in water. More CO2 in water - more carbon acid will be formed by CO2 and water (CO2 + H2O = H2CO3) More H2CO3 in water at a given pH - more HCO3 will be formed (one H ion will acidify the water) - more HCO3 in the water (given pH) more CO3 will be formed (another H ion to the water) And because the <=> arrows - the process will go the opposite way if CO2 will be taken up from the water (either by photosynthesis or at the air/water interface (skimmers create a huge air/water interface) if the CO2 concentration in water is higher than the equilibrium point air/water is at a given pH.

The whole thing with ocean acidification and pH swing in an aquarium is expressed in the few line above. Or in this two equations

CO2<=>H2CO3 <=> HCO3 <=> CO3.

CO2 air <=> CO2 water

Do you not understand it - no worry - it have take me nearly a whole life to be able to understand it by myself - and I probably not understand the whole process either.

Sincerely Lasse

 

[Lasse]

@Randy Holmes-Farley Your calculations in the table is based on an alkalinity of 8 dKH. Are there any significant differences between the species if the alkalinity is 7, 8, 9 ,10 or 11 dKH or is it nearly the same ?

Sincerely Lasse

 

[Xero]

People always tell me i'm crazy for running my tanks like this, and admittedly, i only run some of them this way, but, i've had more growth with this method than almost anything else. They say don't chase ph?? naw, chase ph, with kalk...why not. PH shutoff which doses kalk or RODI depending. The only real black magic is figuring out what the PH shutoff needs to be to get to a target alk/cal range, but, with appropriate timeouts on my doser, i've made this quite safe.

Oddly enough, i'm wondering if your table might have answered the "black magic" bit some more

and here's the tank in question.

 

[Lasse]

I did a quick calculation of possible C fixation from CO2 in my aquarium during 3.5 hours without skimming in my own aquarium. Based on pH rise and the tables publicated in this thread. The result indicate a minimum of around 0.4 - 0,6 mg C fixation from CO2 during these circumstances. IMO it is very low in my rather dense populated (with softies, LPS and SPS corals) aquarium. I will investigate this further on.

Sincerely Lasse

 

[Randy Holmes-Farley]

@Randy Holmes-Farley Your calculations in the table is based on an alkalinity of 8 dKH. Are there any significant differences between the species if the alkalinity is 7, 8, 9 ,10 or 11 dKH or is it nearly the same ?

Sincerely Lasse

Everything scales up and down exactly with dKH. So at 7 dKH, everything is 7/8 of what it is at 8 dKH.

 

[Randy Holmes-Farley]

I did a quick calculation of possible C fixation from CO2 in my aquarium during 3.5 hours without skimming in my own aquarium. Based on pH rise and the tables publicated in this thread. The result indicate a minimum of around 0.4 - 0,6 mg C fixation from CO2 during these circumstances. IMO it is very low in my rather dense populated (with softies, LPS and SPS corals) aquarium. I will investigate this further on.

Sincerely Lasse

That assumes zero entry of CO2 from the air to the water, though, which seems unlikely.

 

[Randy Holmes-Farley]

RHF - on behalf of the reefing community, thank you once again for making water chemistry accessible and understandable.

Thanks!

 

[Randy Holmes-Farley]

lol, I will have agree with your starting statement about using units of dKH in your carbonate chemistry results

lol

I may be the first person in history to give CO2 concentrations in dKH. lol

 

[thermoJoe]

That assumes zero entry of CO2 from the air to the water, though, which seems unlikely.

And you would also need to account for heterotrophic respiration, which can be estimated over light-dark cycles with the assumption that autotrophic respiration remains unchanged during the cycles, which has been shown to not be true, but it's a good 1st approximation.

 

[Lasse]

That assumes zero entry of CO2 from the air to the water, though, which seems unlikely.

And you would also need to account for heterotrophic respiration, which can be estimated over light-dark cycles with the assumption that autotrophic respiration remains unchanged during the cycles, which has been shown to not be true, but it's a good 1st approximation.

I´m aware of that - therefore I wrote

The result indicate a minimum of around 0.4 - 0,6 mg C fixation from CO2 during these circumstances

But even if I did more than a tenfold miscalculation - IMO - the amount fixed C from CO2 is very low with my coral population.

Here is how the tank look like - its 300 l in display. 35 plus fish and feeding with around 7 cubes of different Ocean Nutrition frozen food (adult artemia, mysis, black mosquito worms and cyclops)

​

But i have some ideas how to do it better

Sincerely Lasse

 

[Wtyson254]

No - they are not taking up hydrogen ions at all IMO - the zooxanthellae in the coral (and other algae) takes up more CO2 gas from the water compared with what is produced of all cell metabolism and transport in the air/water interface (in an aquarium) . The extra hydrogen ions (or more in a scientist way today hydronium) that will show up when CO2 gas is taken away from water comes from the the equilibrium equation of the carbonate system in water.

CO2<=>H2CO3 <=> HCO3 <=> CO3.

And to make more difficult - there is also an equilibrium equation according to CO2 in air and water there the CO2 concentration in water is mostly depended of air concentration. CO2 air <=> CO2 water. More CO2 in air - more CO2 in water. More CO2 in water - more carbon acid will be formed by CO2 and water (CO2 + H2O = H2CO3) More H2CO3 in water at a given pH - more HCO3 will be formed (one H ion will acidify the water) - more HCO3 in the water (given pH) more CO3 will be formed (another H ion to the water) And because the <=> arrows - the process will go the opposite way if CO2 will be taken up from the water (either by photosynthesis or at the air/water interface (skimmers create a huge air/water interface) if the CO2 concentration in water is higher than the equilibrium point air/water is at a given pH.

The whole thing with ocean acidification and pH swing in an aquarium is expressed in the few line above. Or in this two equations

CO2<=>H2CO3 <=> HCO3 <=> CO3.

CO2 air <=> CO2 water

Do you not understand it - no worry - it have take me nearly a whole life to be able to understand it by myself - and I probably not understand the whole process either.

Sincerely Lasse

In my attempt to understand it, I have tried to apply human (blood) acid/base regulation to sea water. My thought process was that photosynthesis was causing an uptake of CO2 driving the CO2/carbonic acid equilibrium towards the production of CO2 + H2O. In order for the equation to work, bicarbonate would need to scavenge an H+ in order to be converted back to CO2 and H2O.

It is for these reason that we hyperventilate (on a ventilator) patients with severe metabolic acidosis so that CO2 is blows off, with a resulting PH increase. (We would also administer bicarbonate to the patient)

 

[Lasse]

In my attempt to understand it, I have tried to apply human (blood) acid/base regulation to sea water. My thought process was that photosynthesis was causing an uptake of CO2 driving the CO2/carbonic acid equilibrium towards the production of CO2 + H2O. In order for the equation to work, bicarbonate would need to scavenge an H+ in order to be converted back to CO2 and H2O.

It is for these reason that we hyperventilate (on a ventilator) patients with severe metabolic acidosis so that CO2 is blows off, with a resulting PH increase. (We would also administer bicarbonate to the patient)

Yes - but I maybe misunderstand your claim and exclude "in some way"

In some way corals/photosynthesis is taking up H+ during the day...

Its - as you say in your latest post - the reaction CO3 -> HCO3 -> H2CO3 -> CO2 that absorb H ions and convert them into water. i read your statement and thought that you believe that the coral/photosynthesis by itself took up H ions. I´m sorry for that - I do not disagree with your latest statement and example - that´s the way it works

Sincerely Lasse

 

[Randy Holmes-Farley]

In my attempt to understand it, I have tried to apply human (blood) acid/base regulation to sea water. My thought process was that photosynthesis was causing an uptake of CO2 driving the CO2/carbonic acid equilibrium towards the production of CO2 + H2O. In order for the equation to work, bicarbonate would need to scavenge an H+ in order to be converted back to CO2 and H2O.

It is for these reason that we hyperventilate (on a ventilator) patients with severe metabolic acidosis so that CO2 is blows off, with a resulting PH increase. (We would also administer bicarbonate to the patient)

Just to make sure we all agree... photosynthesis overall takes up CO2, and impacts pH that way, it does not take up H+ or release H+. The CO2 itself impacts pH, but direct consumption of H+ (at least without an equal amount of released H+) would increase alkalinity, and that is not observed.

Calcification (formation of calcium carbonate) in general will tend to lower pH because when you take away carbonate (regardless of the molecular level steps to get there), the remaining bicarbonate and carbonate come to a new equilibrium, with some bicarbonate becoming carbonate by Le Chatlier's principle, releasing H+.

HCO3- <---> CO3-- + H+

 

[Cory]

What im curious is based on Randys graph, whats best? High ph, or?

 

[Randy Holmes-Farley]

What im curious is based on Randys graph, whats best? High ph, or?

I think the answer requires a better formed question: better for what?

We know higher alk makes many hard corals grow faster. Is that better?

Hardiness? Growth? Color?

And then, of course, the answer likely isn't well established and call out for experimentation!

 

[Cory]

I think the answer requires a better formed question: better for what?

We know higher alk makes many hard corals grow faster. Is that better?

Hardiness? Growth? Color?

And then, of course, the answer likely isn't well established and call out for experimentation!

Yes i agree. I would want growth, as id think an organism survives best when growing. But a coral that grows fast is likely healthy as an assumption because its needs are being met imo. If it isnt growing, it is succumbing or barely surviving.

Color is complicated and related to nutrients imo. Zoox density. Some might want to tweak color, but it doenst mean its healthy because it looks bleached. I think there is a sweet spot or fine balance between nutrient density.

Hardiness implies healthy. A coral is healthy if its growing imo. What do you think?

I seen an article that said the main driving factor of coral growth in seawater was temperature. I wonder what temperature does with your graph?