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.