Substrate question.

[Nont]

I realised that there is rotten smell every single time I use 6cm+ deep gravel substrate, which I think indicates anaerobic gas. There are also loads of mulm and detritus under the substrate which I can’t vacuum it because of carpeting plants. That got me questioning if having an anaerobic zone under the substrate make plant suffer from Nitrogen deficiency? And will mulm and detritus under substrate going to cause a problem to the inhabitat in the future?

 

[_Maq_]

Anaerobic conditions in the substrate are normal and plants are not only adapted to it, they outright expect it. That said, it has it's limits.
Generally, the more plants and more oxygen in the water column, the better. Conversely, the more you feed the higher biological oxygen demand (BOD) and the higher the danger of tank collapse due to low oxygen.

 

[Nont]

Anaerobic conditions in the substrate are normal and plants are not only adapted to it, they outright expect it. That said, it has it's limits.
Generally, the more plants and more oxygen in the water column, the better. Conversely, the more you feed the higher biological oxygen demand (BOD) and the higher the danger of tank collapse due to low oxygen.

Yes, I am aware of that, but my concern is whether the rotten egg smell (Hydrogen sulfide?) in the substrate indicates that denitrification is occuring. Would that result in nitrogen deficiency in plants.

Speaking of aeration, I would like to know if adding airstone to the tank lowers the amount of CO2 in water?

 

[_Maq_]

whether the rotten egg smell (Hydrogen sulfide?) in the substrate indicates that denitrification is occuring.

As redox decreases, microbes respire nitrites first (that's denitrification), then iron and manganese, and then sulfates. Sulfate reduction results in hydrogen sulfide.
So, yes, if sulfate reduction occurs, denitrification presumably precedes it.

if adding airstone to the tank lowers the amount of CO2 in water?

If you inject CO2, yes. If you don't inject, well, maybe. I aerate permanently.
However, if you can smell rotten eggs, oxygen is probably much higher priority in your tank than carbon dioxide.

 

[Andy Pierce]

Speaking of aeration, I would like to know if adding airstone to the tank lowers the amount of CO2 in water?

Adding an airstone accelerates the process by which the CO2 dissolved in the water reaches equilibrium with atmospheric CO2 gas. For the CO2 dissolved in water that is about 0.5 PPM. This works in both directions: dissolved CO2 higher than 0.5 PPM gets lowered and dissolved CO2 lower than 0.5 PPM gets raised. In any event, I think aeration is good to have so I run airstones regardless of whatever that might do to CO2.