Alkalinity stability? pH stability? Are they even different?

[Randy Holmes-Farley Verified Community Expert]

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.

How stable is the alkalinity doing this?

 

[Xero]

How stable is the alkalinity doing this?

It's always been pretty stable, but, I haven't setup a trident on it (yet!! I have one.) So that answer's only as good as my weekly testing tells me. I can say, it hasn't killed my SPS with alk spikes or anything like that. A failed PH probe is always a concern, but that leads me to my next safety mechanism. Both heads on the DOS are setup with code, not with a dosing schedule, and in my code is a "when" statement that prevents either of them from "long-running" and it throws an error if they do. 9 times out of 10, if I start hitting this "when" statement more than normal - It's usually a sign that my kalk reactor is running low, and alk/cal usually start to run lower at that point. "Other issues" take up that remaining 1/10. Like the time my kalk dosing tube got clogged up!

I've definitely come up with a method to this madness. I just don't know how well it will scale. That's my next experiment, though. I'm building a large system with a very large kalk stirrer, and I plan to try and scale this as far as it will safely go. I'll purposely increase evaporation, if need be.

 

[Cory]

It's always been pretty stable, but, I haven't setup a trident on it (yet!! I have one.) So that answer's only as good as my weekly testing tells me. I can say, it hasn't killed my SPS with alk spikes or anything like that. A failed PH probe is always a concern, but that leads me to my next safety mechanism. Both heads on the DOS are setup with code, not with a dosing schedule, and in my code is a "when" statement that prevents either of them from "long-running" and it throws an error if they do. 9 times out of 10, if I start hitting this "when" statement more than normal - It's usually a sign that my kalk reactor is running low, and alk/cal usually start to run lower at that point. "Other issues" take up that remaining 1/10. Like the time my kalk dosing tube got clogged up!

I've definitely come up with a method to this madness. I just don't know how well it will scale. That's my next experiment, though. I'm building a large system with a very large kalk stirrer, and I plan to try and scale this as far as it will safely go. I'll purposely increase evaporation, if need be.

Whats your alkalinity at with ph that high consistently?

 

[Lasse]

According to the question of primary (major) inorganic C source pathway for photosynthesis - this experimental tank can be of interest to follow. Its a pure macro Algae tank and he had noted a decline in alkalinity and have some ideas of testing CO2 adding in the future

https://www.reef2reef.com/threads/nano-macroalgea-tank.707755/
Sincerely Lasse

 

[Xero]

Whats your alkalinity at with ph that high consistently?

I usually target 8-9 alk / 420-440 cal. It drops to 7-ish when the kalk stirrer is running low...The PH shutoff is what determines this, though. So even though it seems high, it's basically where it needs to be to get to those levels. I really should put the trident on this tank so I can overlay the graphs. It would make this a lot more interesting....

On a side note, I run a small coral QT tank this same way, but it has a 150w DE halide on it. The halide seems to be causing this gigantic PH spike every day, and the shut-off has to be much higher on that tank to compensate. I also reloaded the kalk-stirrer a few days ago, and you can see the direct impact this had on the graph, which is kind of interesting. I've never had too much trouble with this tank either, but there are definitely bigger spikes here due to the halide/fans running. I'm considering creating a schedule to avoid dosing it during the halide peak, maybe only dosing it at night.

 

[Randy Holmes-Farley Verified Community Expert]

According to the question of primary (major) inorganic C source pathway for photosynthesis - this experimental tank can be of interest to follow. Its a pure macro Algae tank and he had noted a decline in alkalinity and have some ideas of testing CO2 adding in the future

https://www.reef2reef.com/threads/nano-macroalgea-tank.707755/
Sincerely Lasse

How does that bear on the carbon source?

Even if it used bicarbonate or carbonate, photosynthesis cannot consume alkalinity.

 

[Larry L]

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.

Just trying to understand the setup - looks like basically you're making your ATO do the topoff either with RO or with kalk, depending on whether the pH is above or below your setpoint?

 

[Xero]

Just trying to understand the setup - looks like basically you're making your ATO do the topoff either with RO or with kalk, depending on whether the pH is above or below your setpoint?

Yes, basically that.

I could probably post the code if people are really curious, but was trying to avoid going too far off-topic. It's got a ton of shut-offs and fail-safes, and it's definitely a DIY ATO, if you want to call it that. I run dual or triple floats off the apex breakout box, preferably one that's attached directly to the head unit, as this avoids the various corruption issues I experienced with the FMM/ATK module. The pumps are just dosers capable of higher-than-average volumes - either the DOS on my 29g, or a DIY 2-headed doser I made on the coral QT, just plugged into 2 outlets of an EB4.

 

[biom]

Thank you Randy for this questions and for this thread, because the coral calcification process is as you said "dogma" and most of the valuable scientific information on the topic is somehow "diluted" because of many recent articles dedicated to ocean acidification.

But before go deeper in this first to stress one important fact often omitted even here.

The calcification process in corals happens in a isolated space called subcalicoblastic space. Entrance of any kind of ions in it is almost fully controlled. In this space pH is higher than of ambient sea water and in different species can vary from 8.5 up to 10 in some deep water species and it is pretty stable. So calcification in corals happens in a controlled environment with pH 8.5 or more and elevated levels of DIC. The one can said OK but then this space is surrounded by ambient seawater with certain pH could influence transport, well no, actually next to calcification space there is another space called coelenteron in which pH is again different than seawater, but this time it is more acidic, has some gradient and could be as low as 6.6 - 7 pH close to the membrane of the calcification space (because of H+ transport from calcification liquid). So the calcification space in corals is surrounded by water with pH around 7 or even less, and we need to take into consideration when talking about calcification process in corals.

Before you ask for references I'm sure I have some :) maybe it worth to make an layman (from layman also) article with some drawings but not sure if I can do it in this forum or I need to have different level membership.

Experimentally, higher pH appears to accelerate calcification for some corals. The question is why.

It might be because it is much easier to pump out the H+ needed for calcification (for two reasons, to convert bicarbonate into carbonate, and to otherwise raise the pH in the region of the coral where calcium carbonate deposition is actually taking place).

It might also be, as mentioned above, that corals might actually take up carbonate, despite the evidence suggesting it is bicarbonate.

It is even harder to pump out protons, because Ca2ATP pumps are doing this actually from closed environment with pH 8.5 or more to a semi-closed space with pH around 7 or lower, but not in the ambient seawater with said 8.0 - 8.1 pH

Given that it is quite possible most (but not all) of carbon needed for calcification enter calcification fluid as CO2 (instead of active transport of HCO3 or CO3) via diffusion caused by different partial pressure of CO2 on both sides of membrane.

 

[Lasse]

How does that bear on the carbon source?

Even if it used bicarbonate or carbonate, photosynthesis cannot consume alkalinity.

I leave this topic in this thread in order to not going too much of topic - however I will try to explain myself in the Nano Macro Tank there it will be more on topic

Given that it is quite possible most (but not all) of carbon needed for calcification enter calcification fluid as CO2 (instead of active transport of HCO3 or CO3) via diffusion caused by different partial pressure of CO2 on both sides of membrane.

Is this a possible pathway for C transport for photosynthesis process in high alkaline plants and algae too? Beside/instead of the use of carbonic anhydrase? As I understand it is believed that the conversion of HCO3 into CO2 in corals happens in the animal part of the relationship close to the symbiont?

Sincerely Lasse

 

[biom]

Is this a possible pathway for C transport for photosynthesis process in high alkaline plants and algae too? Beside/instead of the use of carbonic anhydrase? As I understand it is believed that the conversion of HCO3 into CO2 in corals happens in the animal part of the relationship close to the symbiont?

thank you, interesting question. Not sure what you mean high alkaline plants, is that terrestrial ones inhabiting alkaline soils? If yes not sure, but possible.
About algae, yes this could be possible pathway for calcareous algae (like coralline ) which tend to deposit calcareous material in their cell walls.

As I understand it is believed that the conversion of HCO3 into CO2 in corals happens in the animal part of the relationship close to the symbiont?

Yes, in the coelenteron of the animal part very close to the symbiont alga. Possibly this is one of the reasons why scleractinian (or stony) corals actually build calcium carbonate "skeletons" - proton secretion as result of calcification helps algae to take CO2 in more energy efficient way.

And second explanation why corals are precipitate calcium carbonate could be this proton secretion stimulates nutrient uptake by causing cell membrane electrical potential attracting cations NH4 and taking up anions like NO3 and PO4, similar to plants does. This could explain why corals thriving well in waters very poor in nutrients. Actually the terrestrial plants inhabiting alkaline and poor of nutrients soils does something very similar, they precipitate calcium oxalate in the roots and secreting protons which makes nutrient much more available.

 

[serwobow]

As expected, a drop of 0.3 pH units is about a doubling of CO2.

pH	HCO3- (dKH)	CO3— (dKH)	CO2 (in “dKH”)
7.60​	7.54​	0.28​	0.1324​
7.65​	7.52​	0.31​	0.1170​
7.70​	7.49​	0.35​	0.1033​
7.75​	7.46​	0.39​	0.0911​
7.80​	7.42​	0.44​	0.0803​
7.85​	7.37​	0.49​	0.0706​
7.90​	7.31​	0.54​	0.0621​
7.95​	7.25​	0.61​	0.0544​
8.00​	7.18​	0.67​	0.0477​
8.05​	7.10​	0.75​	0.0417​
8.10​	7.01​	0.83​	0.0364​
8.15​	6.92​	0.92​	0.0317​
8.20​	6.81​	1.01​	0.0275​
8.25​	6.70​	1.12​	0.0239​
8.30​	6.57​	1.23​	0.0207​
8.35​	6.44​	1.35​	0.0178​
8.40​	6.29​	1.48​	0.0153​
8.45​	6.13​	1.62​	0.0131​
8.50​	5.97​	1.77​	0.0112​
8.55​	5.79​	1.93​	0.0096​
8.60​	5.60​	2.09​	0.0081​

Thank you for this chart and discussion Randy! Maybe this was already mentioned, but I didn't see it, but is one implication of this chart : that one could potentially slow algae growth (which primarily utilizes CO2) by maintaining a pH around 8.2?
My own tank pH ranges from 7.6 (morning) to 8.2 (afternoon). Interesting to think that if I could maintain pH 8.2, algae would find its essential CO2 about 5-fold less abundant during much of the day.

 

[Lasse]

Not sure what you mean high alkaline plants

I mean freshwater plants that thrive in alkaline water - like the great lakes of Eastern Africa and some lakes and water systems in Central America. Some species from the genus Vallisneria as an example

Sincerely Lasse

 

[biom]

[

I mean freshwater plants that thrive in alkaline water - like the great lakes of Eastern Africa and some lakes and water systems in Central America. Some species from the genus Vallisneria as an example

Ahh, of course. I don't know if aragonite precipitation is ever registered in higher plants world and don't know if in this lakes there is enough calcium ions to make the process possible and energy efficient.

 

[Brendank]

Thank you Randy for this questions and for this thread, because the coral calcification process is as you said "dogma" and most of the valuable scientific information on the topic is somehow "diluted" because of many recent articles dedicated to ocean acidification.

But before go deeper in this first to stress one important fact often omitted even here.

The calcification process in corals happens in a isolated space called subcalicoblastic space. Entrance of any kind of ions in it is almost fully controlled. In this space pH is higher than of ambient sea water and in different species can vary from 8.5 up to 10 in some deep water species and it is pretty stable. So calcification in corals happens in a controlled environment with pH 8.5 or more and elevated levels of DIC. The one can said OK but then this space is surrounded by ambient seawater with certain pH could influence transport, well no, actually next to calcification space there is another space called coelenteron in which pH is again different than seawater, but this time it is more acidic, has some gradient and could be as low as 6.6 - 7 pH close to the membrane of the calcification space (because of H+ transport from calcification liquid). So the calcification space in corals is surrounded by water with pH around 7 or even less, and we need to take into consideration when talking about calcification process in corals.

Before you ask for references I'm sure I have some :) maybe it worth to make an layman (from layman also) article with some drawings but not sure if I can do it in this forum or I need to have different level membership.




It is even harder to pump out protons, because Ca2ATP pumps are doing this actually from closed environment with pH 8.5 or more to a semi-closed space with pH around 7 or lower, but not in the ambient seawater with said 8.0 - 8.1 pH

Given that it is quite possible most (but not all) of carbon needed for calcification enter calcification fluid as CO2 (instead of active transport of HCO3 or CO3) via diffusion caused by different partial pressure of CO2 on both sides of membrane.

Biam, there are numerous studies that show the pH of the subcalicoblastic is not independent of the ambient seawater.

 

[Brendank]

Biam, there are numerous studies that show the pH of the subcalicoblastic is not independent of the ambient seawater.

Furthermore, the pH of the subcalicoblastic is species specific and the relationship between seawater pH and the subcalicoblastic pH is also species specific. Further complicating the picture, there are proposed theories that the H+ pump might dominate to rid of the excess for moderate acidification and other mechanisms for more severe acidification.

 

[Randy Holmes-Farley Verified Community Expert]

Thank you Randy for this questions and for this thread, because the coral calcification process is as you said "dogma" and most of the valuable scientific information on the topic is somehow "diluted" because of many recent articles dedicated to ocean acidification.

But before go deeper in this first to stress one important fact often omitted even here.

The calcification process in corals happens in a isolated space called subcalicoblastic space. Entrance of any kind of ions in it is almost fully controlled. In this space pH is higher than of ambient sea water and in different species can vary from 8.5 up to 10 in some deep water species and it is pretty stable. So calcification in corals happens in a controlled environment with pH 8.5 or more and elevated levels of DIC. The one can said OK but then this space is surrounded by ambient seawater with certain pH could influence transport, well no, actually next to calcification space there is another space called coelenteron in which pH is again different than seawater, but this time it is more acidic, has some gradient and could be as low as 6.6 - 7 pH close to the membrane of the calcification space (because of H+ transport from calcification liquid). So the calcification space in corals is surrounded by water with pH around 7 or even less, and we need to take into consideration when talking about calcification process in corals.

Before you ask for references I'm sure I have some :) maybe it worth to make an layman (from layman also) article with some drawings but not sure if I can do it in this forum or I need to have different level membership.

No need for references. i certainly agree that is the basic process. Many authors think the carbon diffuses through the organism as CO2. No one I have seen, however, suggest that is it comes from the surrounding seawater as CO2 at that elementary step of the process.. :)

 

[Randy Holmes-Farley Verified Community Expert]

Thank you for this chart and discussion Randy! Maybe this was already mentioned, but I didn't see it, but is one implication of this chart : that one could potentially slow algae growth (which primarily utilizes CO2) by maintaining a pH around 8.2?
My own tank pH ranges from 7.6 (morning) to 8.2 (afternoon). Interesting to think that if I could maintain pH 8.2, algae would find its essential CO2 about 5-fold less abundant during much of the day.

Some algae slow in growth as pH rises due presumably to limiting CO2. Some do not, and the explanation is that they use bicarbonate as a source of CO2 (although they do not deplete alkalinity since the pump out OH-. I discuss that in this article and show a bunch of data for different species:

Photosynthesis and the Reef Aquarium, Part I: Carbon Sources by Randy Holmes-Farley - Reefkeeping.com

from it:
Table 1. Relative rates of photosynthesis in seawater (measured by oxygen evolution) at pH 8.7 relative to pH 8.0. A value of 100 means that the rates were the same, and values below 100 indicate less photosynthesis at pH 8.7.

Species of macroalgae:	Relative photosynthesis at pH 8.7 compared to pH 8.1 (as a %):
Chaetomorpha aerea	75
Cladophora rupestris	100
Enteromorpha compressa	67
Ulva rigida	100
Codium fragile	76
Asparagopsis armata	45
Gelidium pusillum	33
Gelidium sesquipedale	18
Gymnogongrus sp.	39
Osmunda pinnatifida	46
Porphyra leucosticta	110
Fucus spiralis	86
Colpomenia sinuosa	100
Dictyota dichotoma	53
Cystoseira tamariscifolia	57
Padina pavonia	53

 

[taricha]

For folks who are interested in details of these sorts of calculations, they can be found in calculations for Bjerrum plots of carbonate in seawater, which is easy to find online and not that hard to put into excel.

If you're a spreadsheet type, here's one I ran across that does the calcs, if you want to find, say your CO2 water equilibrium level at a particular pH and Alk. (Calibrate your pH to +- 0.1 first, or it's not very worthwhile.)
Jim gives some details here on parameters to use to make the sheet give sensible numbers.

Just a suggestion: For better accuracy, try the NBS [pH] scale and the GEOSEC or Peng, et. al. constants. It will make a significant difference.

There's a little learning curve to it (Alk in microequivalents/L etc), but it's fun.

 

[Brendank]

There’s an interesting complication to be aware of when calculating the CO2-HCO3-CO3 relationship. There are different pH scales that correspond to different equilibrium constants. Using an inconsistent set will give you the wrong concentrations.