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Does depleted KH stop the nitrogen cycle?

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.
 
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.
 
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
 
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?
 
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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
 
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.
 
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
 
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