Does depleted KH stop the nitrogen cycle?

[Zeus.]

So I think we may be able to agree that little KH not only help keep more stable/safe pH levels for our livestock, a little KH will probably be a safe place to prevent the nitrogen cycle from stalling, which if stalls may result in toxic levels of nitrogen compounds in our tanks. After all we are after a unhindered conversion from amonium compounds to nitrates.

 

[Soilwork]

So I think we may be able to agree that little KH not only help keep more stable/safe pH levels for our livestock, a little KH will probably be a safe place to prevent the nitrogen cycle from stalling, which if stalls may result in toxic levels of nitrogen compounds in our tanks. After all we are after a unhindered conversion from amonium compounds to nitrates.

Stable perhaps yes. Safe I guess that depends. Since we have determined that aquarium filters contain organisms capable of ammonia oxidation in acidic mediums I’m much more confident that we do not have to worry about KH/pH dependant nitrification from stalling. If you wanted to try to control a unknown risk then a little bit of KH is a good idea.

 

[dw1305]

Hi all,

So I think we may be able to agree that little KH

If you wanted to try to control a unknown risk then a little bit of KH is a good idea.

I'd guess that (for most people) that is true, a <"minimal amount of carbonate hardness"> makes tank management easier, partially because you have <"more microbial activity"> in harder water.

Since we have determined that aquarium filters contain organisms capable of ammonia oxidation in acidic mediums I’m much more confident that we do not have to worry about KH/pH dependant nitrification from stalling.

I'd guess that is also true. A few people breed <"black-water"> fish species (Parosphromenus spp., Apistogramma, Heckel Discus etc.) in water without any dKH and @Roland keeps his planted tanks at <"very low dKH values"> (although with more dGH).

cheers Darrel

 

[Soilwork]

So here’s another question. If aquarium filters typically have more COMAMMOX nitrospira and AOA that can operate at lower pH level and don’t typically require KH and prefer ammonium as their nitrogen source, does their processes acidify the water?

 

[dw1305]

Hi all,

So here’s another question. If aquarium filters typically have more COMAMMOX nitrospira and AOA that can operate at lower pH level and don’t typically require KH or prefer ammonium as their nitrogen source, does their processes acidify the water?

It is a good question. I don't know, but I'll see what I can find.

Cheers Darrel

 

[rdk1402]

I feel that fish are typically regarded as passive bystanders that need to be kept in water devoid of ammonia.

In my view, ammonia becomes dangerous when (most) freshwater fish species are no longer able to excrete ammonia through their gills. This happens when the pH in the water column surpasses the pH in the blood.

Certain freshwater fish species hailing from high pH environments have certain mechanisms in place to dispose ammonia via other ways.

If you'd place an average freshwater species in a high pH environment that is devoid of ammonia, it will die because it cannot excrete ammonia (as NH3) and the build-up of NH4 in the body starts messing with K channels.

But I might be mistaken.

 

[dw1305]

Hi all,

In my view, ammonia becomes dangerous when (most) freshwater fish species are no longer able to excrete ammonia through their gills.

Tolerances to ammonia levels definitely differ between fish, there are plenty of references from Aquaculture, where you have extremely sensitive salmonids at one end of the spectrum and Carp and Tilapia at the other (more tolerant) end. The situation is complicated further by the effects of oxygen and CO2 and the <"(Bohr)-Root effect">.

This happens when the pH in the water column surpasses the pH in the blood.

So blood has the same pH as salt water ~ pH8 (we are all still marine organisms in some ways). Once we get into water that has a higher pH than the CO2 ~ carbonate ~ equilibrium point (~pH8) fish have to have adaptations to deal with the greater toxicity of ammonia (all the TAN is NH3), and if the water is warm? That is a double whammy. I know that the Soda Cichlid (Alcolapia alcalicus) <"https://www.seriouslyfish.com/species/alcolapia-alcalicus/"> excretes urea (CO(NH2)2) for example.

Leading on from @Soilwork 's question, this is from <"https://www.pnas.org/doi/full/10.1073/pnas.1010981108"> linked <"earlier in this thread">. It is in soil, but it uses labelled CO2. It is from 2011, so I'll try find some papers that cited it and either agree or disagree.

.......Whether ammonia-oxidizing archaea in soil can assimilate CO2 remains uncertain........... We were able to demonstrate active CO2 fixation and carbon assimilation coupled to ammonia oxidation by archaea in an agricultural soil using an RNA-SIP approach. Archaeal amoA transcripts were labeled consistently during incubation of soil microcosms with 13CO2 and fertilization with either 15 μg or 100 μg (NH4)2SO4-N·g−1 d.w.s. Controls without fertilization and with 12CO2 did not show any labeling, confirming that CO2 fixation was coupled to ammonia oxidation and that labeling resulted from true label incorporation. Analyses of archaeal amoA transcripts and genes from gradient fractions of the microcosms with the lower level of fertilization (15 μg N·g−1 d.w.s.) revealed clear differences and dynamic changes of archaeal ammonia oxidizers representing amoA clusters that differ in activity and in assimilation of carbon..........

I'll see if I can find a paper with the metabolic pathways for microbial nitrification in very acidic conditions.

cheers Darrel

 

[dw1305]

Hi all,
I'll add this here at the moment. <"https://journals.asm.org/doi/full/10.1128/aem.00104-24">. It is quite an interesting paper and worth a read for those interested in this sort of thing.

McKnight MM, Neufeld JD. (2024). "Comammox Nitrospira among dominant ammonia oxidizers within aquarium biofilter microbial communities". Appl Environ Microbiol 90:e00104-24. <"https://doi.org/10.1128/aem.00104-24">

.... Comammox Nitrospira amoA genes were detected in all 38 freshwater biofilter samples (average CMX amoA genes: 2.2 × 103 ± 1.5 × 103 copies/ng) and dominant in 30, whereas AOA were present in 35 freshwater biofilter samples (average AOA amoA genes: 1.1 × 103 ± 2.7 × 103 copies/ng) and only dominant in 7 of them. The AOB were at relatively low abundance within biofilters (average of 3.2 × 101 ± 1.1 × 102 copies of AOB amoA genes/ng of DNA), except for the aquarium with the highest ammonia concentration

..... Network analysis of freshwater microbial communities demonstrated positive correlations between nitrifiers and heterotrophs, suggesting metabolic and ecological interactions within biofilters. These results demonstrate that comammox Nitrospira plays a previously overlooked, but important role in home aquarium biofilter nitrification......

...... The findings reveal that complete ammonia-oxidizing (comammox) Nitrospira were present in all freshwater aquarium biofilter samples in high abundance, challenging our previous understanding of aquarium nitrification. ....

..... Within freshwater aquarium biofilter samples specifically, correlation analysis revealed that aquarium age, general water hardness, and aquarium temperature all correlated significantly with 16S rRNA gene profiles (R2 > 0.3, P < 0.05; Fig. 1B). For freshwater samples, several taxa grouped in the center of ordination space, indicating that they were common to most freshwater biofilter samples, including ASVs affiliated with Comamonadaceae, Vicinamibacteraceae, Rhodobacter, and Terrimonas. In contrast, Blastocatellaceae-associated taxa grouped with samples that had lower general hardness (Fig. 1B), indicating that these bacteria were at higher relative abundances in soft water ....

The paper mentions that some of the aquariums were planted, but doesn't use this as a variable in the analysis. I'll try contacting Josh Neufeld and see if that is an area that interests them.

At some point I'll pull together all the <"nitrifying microbes in aquaria"> posts into a single thread.

cheers Darrel

 

[Heelllooo]

So I think we may be able to agree that little KH not only help keep more stable/safe pH levels for our livestock, a little KH will probably be a safe place to prevent the nitrogen cycle from stalling, which if stalls may result in toxic levels of nitrogen compounds in our tanks. After all we are after a unhindered conversion from amonium compounds to nitrates.

Hi all,


I'd guess that (for most people) that is true, a <"minimal amount of carbonate hardness"> makes tank management easier, partially because you have <"more microbial activity"> in harder water.

I'd guess that is also true. A few people breed <"black-water"> fish species (Parosphromenus spp., Apistogramma, Heckel Discus etc.) in water without any dKH.

The 0kH scare is just a myth that need to be stopped.

I've run a 60L planted tank at 0kH 3gH for a year now. I use DI water + salt so I'm sure there is no kH in it. I never test pH.

I had a spawn of Apisto in it and I raise 80 fry to 4 month and a half in it without any issue at all. I was feeding very heavily and the tank was very overstock by normal standard.

I even inject a little of CO2 with the yeast method which is supposed to be an issue and crash my pH.

 

[Bradders]

So I think we may be able to agree that little KH not only help keep more stable/safe pH levels for our livestock, a little KH will probably be a safe place to prevent the nitrogen cycle from stalling, which if stalls may result in toxic levels of nitrogen compounds in our tanks. After all we are after an unhindered conversion from amonium compounds to nitrates.

I understand that cycling an aquarium becomes problematic (stalls) when the PH goes below 6.5. However, I have not been able to get a clear answer to whether it’s only the initial cycling period that you need to keep the PH above 6.5 and it then becomes less important?

 

[dw1305]

Hi all,

The 0kH scare is just a myth that need to be stopped.

I think it is going to be an uphill struggle.

Cheers Darrel

 

[dw1305]

Hi all,

I understand that cycling an aquarium becomes problematic (stalls) when the PH goes below 6.5.

That isn't actually true, it is true for the ammonia oxidising that were thought to perform nitrification in aquariums, but not for the microbes that actually occur in aquarium filters.

Have a read through the thread, and it links in some of the up to date science.

However, I have not been able to get a clear answer to whether it’s only the initial cycling period that you need to keep the PH above 6.5 and it then becomes less important?

I'd guess that nitrification is more efficient at higher pH and carbonate hardness, purely because you tend to get more microbial activity in those conditions.

I'd also guess that dissolved oxygen levels are more important than anything else

Cheers Darrel

 

[John q]

I understand that cycling an aquarium becomes problematic (stalls) when the PH goes below 6.5. However, I have not been able to get a clear answer to whether it’s only the initial cycling period that you need to keep the PH above 6.5 and it then becomes less important?

It's a good question question @Bradders
What we have to consider is does nitrification stop below a ph of 6.5, simple answer is no, it doesn't, it possibly slows, but doesn't stop. Sure I've posted links to studies about this somewhere.

Anyway, let's look at the facts.

Life functions perfectly well in nature at pH levels far below 6.5, this could be due to the fact that tan is irrelevant at these levels of ph, or it could be related to the fact that bacteria don't prosper in low ph environments, this is why blackwater fish prefer low ph.

Or... It could be that nitrification ceases to exist at these insane ph levels.... 😆 my tank runs from ph 5.6 to a max of 6.8; so I suspect we can chill and relax about carbonate hardness or more accurately alkalinity levels in our tanks and ph when it comes to nitrification.

 

[hax47]

Thanks Darrel for all this information in this thread! I'll need some time to go through all the links you shared.

The 0kH scare is just a myth that need to be stopped.

Technically, if there is CO2 in the water, there will also be some HCO3- (KH). Not necessarily measurable.

....... In addition, CO2 and HCO3− are in a pH-dependent equilibrium and the concentration of HCO3− decreases with a decreasing pH. This is rather paradoxical given the existence of acidophilic AOA, and potentially implies that acidophilic AOA have a very high affinity for HCO3− in order to grow at low pH. The ecological and physiological consequences of these differences are largely unexplored.........

The question is how high that affinity is and if the unmeasurable bicarbonate would be enough.

An additional option could be the <carbonic anhydrase> that could help the bacteria/archaea to produce bicarbonate from CO2 intracellularly with reasonable speed.

 

[Bradders]

I have more questions! 🙂 I am insatiable!!

Or... It could be that nitrification ceases to exist at these insane ph levels.... 😆 my tank runs from ph 5.6 to a max of 6.8; so I suspect we can chill and relax about carbonate hardness or more accurately alkalinity levels in our tanks and ph when it comes to nitrification.

What PH did you cycle your tank at? And how long did to take to cycle at that PH level? I guess my question here is have you cycled a new aquarium at a PH of 4 and within what time frame did it cycle?

Or... It could be that nitrification ceases to exist at these insane ph levels

I think (and the research seems to support this - thanks Darrel) that nitrification would not stop below, say, a PH of 6. Linked to my question above, does the Nitrifying bacteria which is happy to form in very acidic water take longer to produce and therefore make a cycle impracticable (months more than weeks) in the home Aquarium hobby? (Nature excluded as that has had millions of years to get that balance).

I'd guess that nitrification is more efficient at higher pH and carbonate hardness, purely because you tend to get more microbial activity in those conditions.

Is it not more the case that Ammonia and Nitrite is more toxic at higher PH rather than nitrification being more efficient?

 

[hypnogogia]

Is it not more the case that Ammonia and Nitrite is more toxic at higher PH rather than nitrification being more efficient?

Lower pH levels will have a higher concentration of ammonium, and higher pH levels will have higher concentration of ammonia. Ammonia is toxic whereas ammonium isn’t. Nitrite toxicity doesn’t change with pH AFAIK.

 

[hax47]

An additional option could be the <carbonic anhydrase> that could help the bacteria/archaea to produce bicarbonate from CO2 intracellularly with reasonable speed.

Also, the intracellular/cytoplasmic pH of bacteria/archaea remains higher even in acidic environments, so there might be an option for bicarbonate production inside the cells.

 

[Andy Pierce]

The 0kH scare is just a myth that need to be stopped.

Technically, if there is CO2 in the water, there will also be some HCO3- (KH). Not necessarily measurable.

These are not necessarily incompatible. By KH I expect people mostly mean acid-titratable alkalinity (generally carbonate based) and whilst it is true CO2 will make some HCO3- when it does that it will also make an equivalent amount of H+ so the bicarbonate is essentially "pre-titratated" and wouldn't count as alkalinity - it won't provide any pH buffering capacity either. That lack of pH buffering capacity is the 'scary' part since something that adds acidity could in principle push the pH down significantly. That doesn't mean that anything will actually add acidity under normal circumstances and there are certainly multiple reports with pictures on this forum of successful planted tanks people have been running without adding any (titratable) carbonates.

 

[hax47]

By KH I expect people mostly mean acid-titratable alkalinity (generally carbonate based) and whilst it is true CO2 will make some HCO3- when it does that it will also make an equivalent amount of H+ so the bicarbonate is essentially "pre-titratated" and wouldn't count as alkalinity - it won't provide any pH buffering capacity either.

You are right, having bicarbonate does not necessarily mean having KH.

If I am not mistaken, the bicarbonate is not directly involved in the nitrification, but it buffers the H+ ions created during the process. It might be more about the buffering capacity than actually bicarbonate.

Also, the intracellular/cytoplasmic pH of bacteria/archaea remains higher even in acidic environments, so there might be an option for bicarbonate production inside the cells.

.... so this might not be such a good option, after all, the process does not provide buffering capacity by itself.

 

[Zeus.]

The 0kH scare is just a myth that need to be stopped.

The myth/advise came from our peers/science, a little kH helps to make CO2 injection easier if you are doing a pH profile, I have never injected CO2 into water without any kH so I take there word and the science behind it, plus I don't see what harm a little kH may do and it's cheap enough to add a little kH also.

But good to hear that kH isnt needed for nitrogen cycle