denitrification works at any depth?

[hlama]

hey everyone. after much research i found (and see it in my tanks) denitrification takes place in the no matter the grain size or depth of the sandbed. so why is it that everyone says you need at least 4" depth sandbed for it to be effective?

at first i could see the rational but after looking into it the rational no longer fits. so someone please help to understand this.

ok so DN take place no matter the depth or size of sand. so the depth only adds to amount of DN taking place, mainly because surface area. with live rock, skimmer and macros how much DN do we need. i mean if we go DSB 5" will we not just shift the DN from mainly the rock to mainly the sand? and shift the organic break down uptake from the skimmer, macro and rock to the sand. would not the only real difference be the measurement of nitrate, phos ect.. meaning with a DSB the same amount of "stuff" is present its just where it is that really changes. so using SSB and live rock you get the same DN and the same nitrates and things are present. its just the nitrates have to enter the water colum before the anaerobic bac in the rock can get to it. with BB the rock acts the same as a DSB, because of close prox. of nitrification bac and DN bac. it appears to have less nitrates. ammonia and other organics might remain in the water colum longer depending of flow. still in the end either way would balance right?? even wet,dry bio balls and LR would balance. so what up with the 4" min. thing. it doent make sence, unless you only useing a DSB with no LR or other .

ok not sure if that all made sence. in a nut shell. with enough good quality LR a SSB will be as effective as a DSB. also, with good skimming and lots of macros the fear of the aerobic bac (nitrification) overwhelming the DN bac can be pretty much be eliminated.

i am thinking most the tests done where just on DSB vs whatever. not reflecting most of our tanks conditions. aswell as most info out there is some what out of date or based on out dated methods that used current info from that time. todoay we much more effective skimmers and lighting for macro and such. here is one kinds recent test/experiment i found. it show no real difference in water chemistry amoung many setups. note that part one is pretty much like most lab experiments, doesnt reflect most hobbist conditions. part two is based on actual tank conditions. here is one conclusion of it (part 2 that is).

Each sediment-based aquarium design appeared capable of handling nutrient inputs up to 0.5 mg / L / day of NH4+ - which is equivalent to a well-stocked reef aquarium. At this input level, final concentrations of ammonia, nitrite and nitrate did not differ significantly among aquaria 1) with or without plenums, 2) containing deep (9.0 cm) or shallow (2.5cm) sediments, or 3) containing coarse (2.0mm) or fine (0.2mm) mean particle sizes.

you can read this long article here.
http://www.advancedaquarist.com/2005/6/aafeature
and part two here.
http://www.advancedaquarist.com/2005/7/aafeature

 

[Randy Holmes-Farley]

I do not know if there was significant denitrification (conversion of nitrate into N2) in any of the systems he tested. Consequently, it may not be possible to relate his experiments to denitrification ability.

It is certainly known in the scientific literature that denitrification in natural sediments takes place deeper down.

 

[Monkey_Bone]

"i mean if we go DSB 5" will we not just shift the DN from mainly the rock to mainly the sand? and shift the organic break down uptake from the skimmer, macro and rock to the sand."

In short no.
The skimmer pulls out particulate matter that break down and cause trates and trites not remove trites or trates. The LR will still hold the same amount of bacteria, the macro algae is the only thing that may hurt a little.

The object and the very thing you achieve when you add a DSB or DAB is MORE volume of this beneficial bacteria.
Think of it like adding a refugium. More ter volume and more beneficial bacteria.
Same principle.

And it is a scientificly proven fact that the D/N process takes place in the lower levesl of the sand bed.
Thats why you see tiny bubbles rising up through it.

 

[hlama]

i dont of the exact measurment of DN but in the end all tanks had similar water chemistry. one can only assume (i know bad word) that DN has taken place in all the tanks. i do see it takeing place in one of my tanks with a 1" sandbed. i would think most tanks have less O2 flowing accross the sand bed than in the natural ocean, that might have something to do with it might not. even so with enough LR and a SSB it would balance out over time, right? so, is the difference of a SSB vs a DSB is just where you are providing the surface area for each bac, either in LR or sand. so with a DSB your just not useing the surface area in the LR. with a SSB your counting on the LR?

it just seema that all the data used is based on tanks with nothing else other than various depths of sandbeds, no rock. so yeah sure a DSB is better than SSB but what about adding LR to the equation, and the amount of LR with both a DSB and SSB. this is the only test i found that does something like that and the water chemistry was the same in the end.

 

[hlama]

And it is a scientificly proven fact that the D/N process takes place in the lower levesl of the sand bed.

yes no dout here. but that does not mean it doesnt take place in shallower sand, just not as much. depending on the grains each grain can provide some surface area for anaerobic growth, just like LR.

i know this so wide open for debate. but after reading the article and seeing DN in my 1" sandbed. this tank also has LR and chemistry is great. no skimmer nothing but powerheads, 1" sandbed and LR. tanks been going for 5-6 years.

 

[Randy Holmes-Farley]

but in the end all tanks had similar water chemistry. one can only assume (i know bad word) that DN has taken place in all the tanks.

Or none. Lots of processes use nitrogen, not least of which is simple bacterial growth. That's why vodka works, and it is not denitrification. How do we know that didn't happen here?

 

[futrtrubl]

Plus the 9cm used for the DSB isn't exactly deep.

Edward

 

[Monkey_Bone]

You also need to get away from thinking that a DBS will decrease the amount of bacteria present on the LR.
It ill not
It simply means more surface area, and sub-surface area ( is that even a term used? LOL!!)
for MORE bacteria to grow. It will NOT stabelize back to what is was before you added a DBS, or decrease the amount present on the rock.

 

[CaptiveReef]

Bacteria

Bacteria

<a href=showthread.php?s=&postid=7538503#post7538503 target=_blank>Originally posted</a> by Monkey_Bone
You also need to get away from thinking that a DBS will decrease the amount of bacteria present on the LR.
It ill not
It simply means more surface area, and sub-surface area ( is that even a term used? LOL!!)
for MORE bacteria to grow. It will NOT stabelize back to what is was before you added a DBS, or decrease the amount present on the rock.

Yes Monkey_Bone is correct, the only way to decrease bacteria populations, is to remove the bioload (aquatic life) also live rock itself will provide enough bioload to maintain bacteria populations.

CaptiveReef