Shouldn't we mimic nature also concerning alkalinity?

[JonasRoman]

When we talk about parameters, we mostly agree that we should mimic nature, (maybe with one exception, the ratio of nitrogen/phosphorus could be a little higher, like 100 instead of 16).

But when it comes to alkalinity, there's a common sense that you should be a little higher than nature. We have, for instance, The Red Sea Company that proclaim a programme with super high, abnormal levels to increase growth.

I would say that it's best to be slightly above 7 and not too much higher. Thanks to my own devices, like Alkatronic, I have monitored and done thousands of KH measurements with just a few hours between, since 8 years back. This is not a scientific observation, just an observation, but in my systems, I am confident that I can see a healthier tank overall when I'm more close to 7.

Bicarbonate is crucial for determining the stability of the pH, but also the ability for the organism to keep its intracellular pH. Maybe the cell struggles with that if hco3 is too high? In human that is the case and hco3 is very regulated and should not be either too high or low.

Another observation in my tank, in the last year, I haven't had the slightest issue with dinoflagellates or cyano but constantly white sand.. That is also interesting; it's not impossible that it is connected to the 7.0 KH and also the stability around that.

I think it's impossible to prove this because everything is very multifactorial, but the pH is an extremely crucial parameter for the living cell and the hco3 is tightly connected to that, and my tank have never been this stable ever before. So its tempting to associate this with what I now do different.
Also, the coral grows fast enough, and colour is vivid. So KH 7.0 ish is for me with no doubt my new ref value for alkalinity.

Jonas

 

[Seregus]

I think you are correct in a way. I think most important is to keep it stable, because it means you are giving ‘food’ for corals to consume enough of what they need and keeping environment around them without changing. So i guess they can adjust since its impossible Alkalinity is exactly the same all around the world, like salinity is not the same, but again, I’m not a scientist so its just my logical guess…

 

[JonasRoman]

I think you are correct in a way. I think most important is to keep it stable, because it means you are giving ‘food’ for corals to consume enough of what they need and keeping environment around them without changing. So i guess they can adjust since its impossible Alkalinity is exactly the same all around the world, like salinity is not the same, but again, I’m not a scientist so its just my logical guess

Yes the stability is very important but my main point is that too high alkalinity maybe is bad for the cells. The importance of Intra cellular PH is something we don't talk about so much , we mostly talk about by carbonate as a supplement for Coral Building. In human blood the hydrogencarbonate concentration is extremely important and we can say that water in the tank is like the human blood, a transporter of elements and it's surrounding the cells and thus affect the cells struggle to maintain the intracellallar pH.
Maybe something is written about this, will search.

 

[JonasRoman]

https://royalsocietypublishing.org/...-calcifying-fluid-pH-is-modulated-by-seawater

In this study We can see proof that alk stability is the key and stability of alkalinity is more important than stability of pH. This is something that at least I have believed in long time but hear we have some scientific evidence aswell.
The study says nothing aboult high levels but it is not a long shot to believe that supra high levels could be damaging as the intracellular pH is very sensitive to small changes in the surrounding hco3 content.

 

[Dan_P]

When we talk about parameters, we mostly agree that we should mimic nature, (maybe with one exception, the ratio of nitrogen/phosphorus could be a little higher, like 100 instead of 16).

But when it comes to alkalinity, there's a common sense that you should be a little higher than nature. We have, for instance, The Red Sea Company that proclaim a programme with super high, abnormal levels to increase growth.

I would say that it's best to be slightly above 7 and not too much higher. Thanks to my own devices, like Alkatronic, I have monitored and done thousands of KH measurements with just a few hours between, since 8 years back. This is not a scientific observation, just an observation, but in my systems, I am confident that I can see a healthier tank overall when I'm more close to 7.

Bicarbonate is crucial for determining the stability of the pH, but also the ability for the organism to keep its intracellular pH. Maybe the cell struggles with that if hco3 is too high? In human that is the case and hco3 is very regulated and should not be either too high or low.

Another observation in my tank, in the last year, I haven't had the slightest issue with dinoflagellates or cyano but constantly white sand.. That is also interesting; it's not impossible that it is connected to the 7.0 KH and also the stability around that.

I think it's impossible to prove this because everything is very multifactorial, but the pH is an extremely crucial parameter for the living cell and the hco3 is tightly connected to that, and my tank have never been this stable ever before. So its tempting to associate this with what I now do different.
Also, the coral grows fast enough, and colour is vivid. So KH 7.0 ish is for me with no doubt my new ref value for alkalinity.

Jonas

Isn’t coral growth and appearance affected by more than alkalinity? For example, can the optimum value of alkalinity be different for a different nitrate, or more generally, inorganic nitrogen, level?

As for the observation about dinoflagellate and cyanobacteria, I cannot think of a reason for a certain alkalinity making their growth less likely.

 

[strich]

Doesn't the alk range depend a bit on how NO3/PO4 rich your system is? For example, my young tank is currently around 60ppm NO3 / 0.55ppm PO4 which I'm aiming to slowly pull down. But it will always push high due to the 11 fish I have in the system and the heavy healthy diet I aim for.

For my system it would seem like I should really be in the 8-9dkh range right? I have the nutrient headroom for it.

 

[EnterName]

Regarding Alkalinity
I know that in high PAR systems you have to control alkalinity to prevent "burnt tips" in SPS. Apparently calcification manages to outperform tissue growth so you have to keep alkalinity lower to slow it down. I have not observed issues when PAR levels are normal and nutrients don't appear to be limiting growth, so I'm not sure if lower alkalinity is actually beneficial.

Regarding Cyanobacteria
I believe they can use bicarbonates as a carbon source, but don't think that's necessary in many tanks with decent organic carbon supply. Even though this hasn't been scientifically proven as far as I know, many people blame excessive dissolved organic carbon for cyano issues.

Regarding N:P ratios:
I assume you are aware, but because it's misused so often I want to mention that 16:1 (Redfield ratio) is not the natural ratio of nitrogen and phosphorus in the water column of coral reefs. It's the ratio of N/P in planktonic biomass.

Depending on the reef, season, and depth you will find various ratios, but apparently 3:1 to 7:1 are considered normal for the actual water column of pristine reefs: https://pmc.ncbi.nlm.nih.gov/articles/PMC9962417/

There are also higher naturally occurring ratios like 30:1 up to 560:1, but this causes reefs to struggle with black band disease, as well as ratios below 3:1: https://www.nature.com/articles/s41467-026-72175-4

 

[Peer.Boerner]

When we talk about parameters, we mostly agree that we should mimic nature, (maybe with one exception, the ratio of nitrogen/phosphorus could be a little higher, like 100 instead of 16).

But when it comes to alkalinity, there's a common sense that you should be a little higher than nature. We have, for instance, The Red Sea Company that proclaim a programme with super high, abnormal levels to increase growth.

I would say that it's best to be slightly above 7 and not too much higher. Thanks to my own devices, like Alkatronic, I have monitored and done thousands of KH measurements with just a few hours between, since 8 years back. This is not a scientific observation, just an observation, but in my systems, I am confident that I can see a healthier tank overall when I'm more close to 7.

Bicarbonate is crucial for determining the stability of the pH, but also the ability for the organism to keep its intracellular pH. Maybe the cell struggles with that if hco3 is too high? In human that is the case and hco3 is very regulated and should not be either too high or low.

Another observation in my tank, in the last year, I haven't had the slightest issue with dinoflagellates or cyano but constantly white sand.. That is also interesting; it's not impossible that it is connected to the 7.0 KH and also the stability around that.

I think it's impossible to prove this because everything is very multifactorial, but the pH is an extremely crucial parameter for the living cell and the hco3 is tightly connected to that, and my tank have never been this stable ever before. So its tempting to associate this with what I now do different.
Also, the coral grows fast enough, and colour is vivid. So KH 7.0 ish is for me with no doubt my new ref value for alkalinity.

Jonas

Appreciate your perspective. It’s definitely worth serious consideration. For full transparency, I’m running Alk at just over 9 with no ill effects but can’t help wondering if things could be better closer to natural levels. Thanks again

 

[JonasRoman]

Isn’t coral growth and appearance affected by more than alkalinity? For example, can the optimum value of alkalinity be different for a different nitrate, or more generally, inorganic nitrogen, level?

As for the observation about dinoflagellate and cyanobacteria, I cannot think of a reason for a certain alkalinity making their growth less likely.

I do not believe there is different optimal alkalinity values depending on nutrients. Alkalinity is an own player as its strictly connected to intracellular pH. With that said, high nutrients maybe lead to more consumption of hco3, but ofcourse we shall replenish for consumption. What I am talking about is the level itself and how that may impact the cell struggles to maintain the intracellular pH.
And the later is extremely crucial for a cell.

 

[Randy Holmes-Farley Verified Community Expert]

I don’t really have an opinion on what is “best”, and I think the answer may depend on your goals.

If one accepts the premise that some hard corals grow faster at higher alk and higher pH, then having them higher than nature may be useful not only to grow the tank faster, but maybe better compete with some types of pests.

 

[JonasRoman]

Regarding Alkalinity
I know that in high PAR systems you have to control alkalinity to prevent "burnt tips" in SPS. Apparently calcification manages to outperform tissue growth so you have to keep alkalinity lower to slow it down. I have not observed issues when PAR levels are normal and nutrients don't appear to be limiting growth, so I'm not sure if lower alkalinity is actually beneficial.

Regarding Cyanobacteria
I believe they can use bicarbonates as a carbon source, but don't think that's necessary in many tanks with decent organic carbon supply. Even though this hasn't been scientifically proven as far as I know, many people blame excessive dissolved organic carbon for cyano issues.

Regarding N:P ratios:
I assume you are aware, but because it's misused so often I want to mention that 16:1 (Redfield ratio) is not the natural ratio of nitrogen and phosphorus in the water column of coral reefs. It's the ratio of N/P in planktonic biomass.

Depending on the reef, season, and depth you will find various ratios, but apparently 3:1 to 7:1 are considered normal for the actual water column of pristine reefs: https://pmc.ncbi.nlm.nih.gov/articles/PMC9962417/

There are also higher naturally occurring ratios like 30:1 up to 560:1, but this causes reefs to struggle with black band disease, as well as ratios below 3:1: https://www.nature.com/articles/s41467-026-72175-4

Very good input. Interesting the variations in NP ratio and that it was that low. Interesting.
One of my own theories lomg time ago was that high alk could feed dino. And maybe cyano. Couldn't find any proof though.

 

[JonasRoman]

I don’t really have an opinion on what is “best”, and I think the answer may depend on your goals.

If one accepts the premise that some hard corals grow faster at higher alk and higher pH, then having them higher than nature may be useful not only to grow the tank faster, but maybe better compete with some types of pests.

You can turn that around aswell: supranormal kh and pH drive the skeleton formation to a speed that soft tissue formation can not catch up. Meaning fast growth is not always same as healthy coral.

 

[Randy Holmes-Farley Verified Community Expert]

You can turn that around aswell: supranormal kh and pH drive the skeleton formation to a speed that soft tissue formation can not catch up. Meaning fast growth is not always same as healthy coral.

That is true. Folks can assess in any given tank if it looks like an issue or not. :)

 

[EnterName]

Very good input. Interesting the variations in NP ratio and that it was that low. Interesting.
One of my own theories lomg time ago was that high alk could feed dino. And maybe cyano. Couldn't find any proof though.

Dinoflagellates and cyanobacteria, are capable of photosynthesis and can use inorganic carbon sources. Symbiodinium sp., for example, use zinc-based carbonic anhydrase enzymes to process CO₂ and HCO₃⁻: https://pmc.ncbi.nlm.nih.gov/articles/PMC59491/

Depending on their host (coral or clam), they seem to prefer either CO₂ or HCO₃⁻, which is interesting. So in theory, it's possible that CO₂ could also boost dinoflagellate growth.


However (anecdotal evidence incoming )...

I run an ultra low nutrient system but rarely do water changes, so dissolved organic carbon (DOC) builds up over time while phosphate and nitrate stay below detectable levels. I confirmed the buildup of DOC using Dan's potassium permanganate method, and more recently with a UV275 TOC/DOC meter, comparing readings over time and after a few large water changes I did recently for a change.

In my tank, dinoflagellates are very predictable. When I stop dosing ammonia and phosphate, they show up in moderate amounts that stay on the substrate or glass and never harm my corals. Once I start dosing again, they disappear. I've seen this happen repeatedly (sometimes by accident) over the 3 years in my system, which has been running for over 6 years. Organic carbon levels didn't seem to change this pattern. It looks like neither organic nor inorganic carbon (like bicarbonates) was the cause or a limiting factor, since both were present in excess most of the time.

There was also a period when I dosed alkalinity manually and sometimes forgot, letting it drop very low (something like 6°dKH). The dinoflagellates didn't seem to care. I never thought to measure differences in alkalinity consumption with and without nutrient dosing, so this is just my own experience and can't be compared to any real experiment or study.

 

[13rodo]

You can turn that around aswell: supranormal kh and pH drive the skeleton formation to a speed that soft tissue formation can not catch up. Meaning fast growth is not always same as healthy coral.

I only recently learned about the difference between natural and aquarium Alk ranges. I used to run between 9-10 and have since reduced to 7-8 (closer to 7). Based on nothing other than my eyes, I feel like the flesh on my LPS is healthier (color and extension). Obviously that is pretty subjective, but I don’t feel like the higher range did much.

 

[EnterName]

I only recently learned about the difference between natural and aquarium Alk ranges. I used to run between 9-10 and have since reduced to 7-8 (closer to 7). Based on nothing other than my eyes, I feel like the flesh on my LPS is healthier (color and extension). Obviously that is pretty subjective, but I don’t feel like the higher range did much.

I assume the potential benefit would be more pronounced for SPS corals where you can basically watch the tips grow from day to day.

 

[13rodo]

I assume the potential benefit would be more pronounced for SPS corals where you can basically watch the tips grow from day to day.

Honestly I didn’t notice much difference in the SPS. But again this is all based on sight. To me I don’t notice anything that would drive me back to the 9-10 range.

 

[JonasRoman]

Dinoflagellates and cyanobacteria, are capable of photosynthesis and can use inorganic carbon sources. Symbiodinium sp., for example, use zinc-based carbonic anhydrase enzymes to process CO₂ and HCO₃⁻: https://pmc.ncbi.nlm.nih.gov/articles/PMC59491/

Depending on their host (coral or clam), they seem to prefer either CO₂ or HCO₃⁻, which is interesting. So in theory, it's possible that CO₂ could also boost dinoflagellate growth.


However (anecdotal evidence incoming )...

I run an ultra low nutrient system but rarely do water changes, so dissolved organic carbon (DOC) builds up over time while phosphate and nitrate stay below detectable levels. I confirmed the buildup of DOC using Dan's potassium permanganate method, and more recently with a UV275 TOC/DOC meter, comparing readings over time and after a few large water changes I did recently for a change.

In my tank, dinoflagellates are very predictable. When I stop dosing ammonia and phosphate, they show up in moderate amounts that stay on the substrate or glass and never harm my corals. Once I start dosing again, they disappear. I've seen this happen repeatedly (sometimes by accident) over the 3 years in my system, which has been running for over 6 years. Organic carbon levels didn't seem to change this pattern. It looks like neither organic nor inorganic carbon (like bicarbonates) was the cause or a limiting factor, since both were present in excess most of the time.

There was also a period when I dosed alkalinity manually and sometimes forgot, letting it drop very low (something like 6°dKH). The dinoflagellates didn't seem to care. I never thought to measure differences in alkalinity consumption with and without nutrient dosing, so this is just my own experience and can't be compared to any real experiment or study.

Would be interesting to see if you can reproduce the pattern that your dino have a tendency to blow up with low P, if you at same time hade also low inorganic and organic carbon.
My system is low in organic carbon and reasonable low in inorganic (at least not high). I have no tendency to either dino or cyano even when N and P goes very low.

Maybe your high DOC (and maybe inorganic) make the system sensitive to low nutrients ?

 

[EnterName]

Dinoflagellates and cyanobacteria, are capable of photosynthesis and can use inorganic carbon sources. Symbiodinium sp., for example, use zinc-based carbonic anhydrase enzymes to process CO₂ and HCO₃⁻: https://pmc.ncbi.nlm.nih.gov/articles/PMC59491/

Depending on their host (coral or clam), they seem to prefer either CO₂ or HCO₃⁻, which is interesting. So in theory, it's possible that CO₂ could also boost dinoflagellate growth.


However (anecdotal evidence incoming )...

I run an ultra low nutrient system but rarely do water changes, so dissolved organic carbon (DOC) builds up over time while phosphate and nitrate stay below detectable levels. I confirmed the buildup of DOC using Dan's potassium permanganate method, and more recently with a UV275 TOC/DOC meter, comparing readings over time and after a few large water changes I did recently for a change.

In my tank, dinoflagellates are very predictable. When I stop dosing ammonia and phosphate, they show up in moderate amounts that stay on the substrate or glass and never harm my corals. Once I start dosing again, they disappear. I've seen this happen repeatedly (sometimes by accident) over the 3 years in my system, which has been running for over 6 years. Organic carbon levels didn't seem to change this pattern. It looks like neither organic nor inorganic carbon (like bicarbonates) was the cause or a limiting factor, since both were present in excess most of the time.

There was also a period when I dosed alkalinity manually and sometimes forgot, letting it drop very low (something like 6°dKH). The dinoflagellates didn't seem to care. I never thought to measure differences in alkalinity consumption with and without nutrient dosing, so this is just my own experience and can't be compared to any real experiment or study.

Would be interesting to see if you can reproduce the pattern that your dino have a tendency to blow up with low P, if you at same time hade also low inorganic and organic carbon.
My system is low in organic carbon and reasonable low in inorganic (at least not high). I have no tendency to either dino or cyano even when N and P goes very low.

Maybe your high DOC (and maybe inorganic) make the system sensitive to low nutrients ?

I would test it but after changing tanks I have to add new sand in small batches to keep phosphate from bottoming out. This keeps introducing more and more silicates which cause diatom stains that could skew the results.

From what I have observed so far is that the dinoflagellate genus changes. First Prorocentrum (I don't know if this was high or low DOC during that time), then Ostreopsis during "high" DOC and now Amphidinium during low DOC. However, I've not yet made a precise Triton N-DOC test or so and can only tell you that those DOC levels are high/low relative to each other. I have no way to translate them to ppm or similar units right now.

I'm still working on something Dan was interested in with regards to the UV275 TOC meters so I will make a Triton N-DOC test asap, but the last time I checked their N-DOC system was broken

 

[BriDroid]

Alkalinity and pH being stable has meant the most and best growth for me. Once I switched to a sodium hydroxide based 2-part and was able to get rid of my CO2 scrubber, my pH stabilized from 8.0 to 8.4 over a 24 hour cycle. My alkalinity stabilized at 8.0 to 8.1 and my growth exploded. I keep my N around 5ppm and my P around 0.05ppm with a sodium nitrate/phosphate solution and my colors really took off too.

Finding a way to keep everything stable is the key to a tank the pretty much runs itself.