Most of the denitrifying bacteria are heterotrophs, and they all need some sort of organic carbon to perform denitrification. There are autotroph denitrificators that don't need organic carbon but they require other specific electron donors - sulfur, hydrogen gas etc., which are not that common in a reef tank. More on the sulfur denitrificators in Randy's article about nitrate.
I have no doubt you manage to keep nitrate very low in your system without dosing OC.
You are right - in old - undisturbed - DSB there is a chance that some processes will produce the needed DOC as alcohols and Carbohydrate´s (sugar is a Carbohydrate) I have been working with processes in fish farms there we use these internal DOC productions as DOC sources for denitrification.
Your right - the C/N/P ratio in our food is often so good that the C from the food should not be limited. But as I see it - much of the C in food (hence in the detritus) is much is more tightly chemically bound in the organic material than N and P - therefore the addition of easily accessible DOC becomes a shortcut for the decomposition.
I´m aware of that - and it has indeed already happens but it was not trough the sand bed - it was when I backflush the plenum and let some of the water in the plenum coming out in the DT. Nowadays - I always clean with a direct flow out from the aquarium - if I need too.
This is because 1.3 mg/l NH4 was spread out evenly for 24 hours - this is about 0,0009mg/L NH4 per minute - too small amount to be measured both for ammonia and resulting nitrite. Maybe if you pour all 1,3 mg/L NH4 at once and start constantly measure nitrite the results would be different.
That is correct to a some extent, but the main reason why our aquariums are organic carbon limited is the cellular respiration where most of organic carbon from the food is lost as CO2 (gas).
Nope - I can´t risk that - see @jda ´s post earlier in this thread. And I do not believe that unlimited DOC create momentary NO2 tops - I think you see them if there is not enough of DOC. Therefore - I will dose half the amount I know works in higher NO3 concentrations. Also - I have followed NH4 and NO2 during constant feeding through 12 hours feeding cycle in eel farms. When the filter was optimal used - NH4 always rise till the feeding was stopped (constant load of NH4) - the NO2 was also rising till 2 hours after feedings stop. When I stopped DOC dosing - I uncovered the mechanisms hidden behind the denitrification - constant production of NH4 in the system. This happens at the same time that I see no increase in NO2, which indicates that my NH4 load is significantly less than my filter capacity can handle, hence it can handle extra NO2 from incomplete denitrification. I think it is important to realize that its not possible the transfer what you see in nature with what you will see in a system constructed to optimize both nitrification and denitrification based on many years of experiences (and some studies) i have measured pure anaerobic system (no coupled nitrification) many times and the NO2 will only be a problem in the start and with to less DOC available. its the same with sulphur denitrification (its a autotrophic denitrification - no need for DOC) - you get NO2 build up in the beginning before you got enough of specialized bacteria.
Ok, of course it's your tank you should not risk anythingNope - I can´t risk that - see @jda ´s post earlier in this thread. And I do not believe that unlimited DOC create momentary NO2 tops - I think you see them if there is not enough of DOC. Therefore - I will dose half the amount I know works in higher NO3 concentrations. Also - I have followed NH4 and NO2 during constant feeding through 12 hours feeding cycle in eel farms. When the filter was optimal used - NH4 always rise till the feeding was stopped (constant load of NH4) - the NO2 was also rising till 2 hours after feedings stop. When I stopped DOC dosing - I uncovered the mechanisms hidden behind the denitrification - constant production of NH4 in the system. This happens at the same time that I see no increase in NO2, which indicates that my NH4 load is significantly less than my filter capacity can handle, hence it can handle extra NO2 from incomplete denitrification. I think it is important to realize that its not possible the transfer what you see in nature with what you will see in a system constructed to optimize both nitrification and denitrification based on many years of experiences (and some studies) i have measured pure anaerobic system (no coupled nitrification) many times and the NO2 will only be a problem in the start and with to less DOC available. its the same with sulphur denitrification (its a autotrophic denitrification - no need for DOC) - you get NO2 build up in the beginning before you got enough of specialized bacteria.
Measurement for the day
NO3
NO2
Tendency is rather clear
Sincerely Lasse
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