Denitrification
- Thread starter mikesreef
- Start date
disc1
-RT * ln(k)
I think it depends on a lot more than just inches of sand. The grain size, the amount of rock over top of it, and the flow over it just to name a few. I think that is why there is such disagreement on the inches thing. So looking for a minimum might not be the best idea. Personally I shot for somewhere in the middle of the range wtih 4" - 5".
Paco
Move Don
I don't believe the "under one inch or over four unless you want disaster" rule. I've had a one to two inch sandbed in several aquariums and it's been fine. More important, I believe, is adequate flow to keep stuff from settling down into the sand.
Mark
While this is true, denitrification won't readily occur while in the presence of oxygen. These facultative bacteria favor aerobic (oxygen) respiration. Hence a deeper sand bed is needed to effectively manage nitrate levels in a tank.
As disc1 states, there's no magic number...it will depend on grain size, flow, etc.
A good resource on DSBs:
http://www.reefcentral.com/forums/showthread.php?t=1652103
"It should be at least four inches deep but no more than six, consisting mostly of fine grains..."
While this is true, denitrification won't readily occur while in the presence of oxygen. These facultative bacteria favor aerobic (oxygen) respiration. Hence a deeper sand bed is needed to effectively manage nitrate levels in a tank.
No a deep sandbed is not needed to effectively manage nitrates. Many do very well wtihout them. There is also a study which concludes grain size and depth beyond an inch don't matter .
The bacteria use the O2 and create anaerobic conditions and move on to the nitrate even within the mulm if organic carbon and some phospahate are available.These necessary nutrients are likely absent or very limited in a deep bed without live critters to move it down and to a lesser extent from some advective flow. Without them hetertrophic bacteria won't grow. Ther won't be very many if any to consume N or take teh O from NO3 enabling the formation of N2 gas. Diffuson alone is too weak to keep many nutrients moving deep into the bed. Anoxia in deep areas may also pose difficulties in a poorly maintanined deep bed. Deep beds do offer much more surface area than shallow ones or rocks and can provide useful habitat but won't host many heterotrophic bacteria very far down without some means to ensure adequate flow into them or channeling and transport by live sand benthic critters.
The link you cited discusses all of this including: some of the specifics of the study, etc. Reading a bit more of the thread might help in making an informed decision as to whether someone want's a dsb or not.
No a deep sandbed is not needed to effectively manage nitrates. Many do very well wtihout them. There is also a study which concludes grain size and depth beyond an inch don't matter .
The bacteria use the O2 and create anaerobic conditions and move on to the nitrate even within the mulm if organic carbon and some phospahate are available.These necessary nutrients are likely absent or very limited in a deep bed without live critters to move it down and to a lesser extent from some advective flow. Without them hetertrophic bacteria won't grow. Ther won't be very many if any to consume N or take teh O from NO3 enabling the formation of N2 gas. Diffuson alone is too weak to keep many nutrients moving deep into the bed. Anoxia in deep areas may also pose difficulties in a poorly maintanined deep bed. Deep beds do offer much more surface area than shallow ones or rocks and can provide useful habitat but won't host many heterotrophic bacteria very far down without some means to ensure adequate flow into them or channeling and transport by live sand benthic critters.
The link you cited discusses all of this including: some of the specifics of the study, etc. Reading a bit more of the thread might help in making an informed decision as to whether someone want's a dsb or not.
I definitely agree, but those that do well are most likely utilizing other denitrifying methods such as macroalgae, ATS, N03 reactors, etc. Otherwise, they're relying on frequent WCs as the primary export method.
If we're strictly comparing relative sand bed depths, then a deeper (more hypoxic) bed is better for denitrification.
I totally agree with this also. There are pros/cons to a DSB and other alternative methods to consider before making a decision. Although the OP wasn't asking whether or not he should use one. Rather, what depth is needed for a (presumably effective) DSB.
mikesreef - as Tom stated, you should definitely do your research first, as it can be tricky to maintain an effective DSB. There are other (IMO better) ways to remove nitrates from your tank.
Last edited:
If we're strictly comparing relative sand bed depths, then a deeper (more hypoxic) bed is better for denitrification.
Sorry for the preceding post ; hit the wrong key.
Yes,more depth can support more denitrifying bacteria since there is more surface to colonize if you can keep it hypoxic(low oxygen, NO3) vs anoxic( no oxygen, no NO3) and insure a supply of nutrients the bacteria need.
Unfortunately ,many beds particularly after several years of accumlation of detritus ,mulm and clumping are packed tight down deep and rather sterile; others may be anoxic with evidence of hydrogen sufide generation.
Many aquariums get enough dentirfication to meet their bioload with live rock alone or live rock and a shallow bed to do the job.
Many earlier writings on sand beds ignored the fact that the denitrifying bacteria are facutative and can live with or without oxygen and gave the impression that oxygen exposure would kill them. Hence, the must be 4 inches or more rule ostensibly to keep oxygen out of certain areas. Truth is if you keep oxygen out, you'll keep other nutrients out too. If you let a little in with other nutrients ,the bacteria will use it up and move on to the NO3.
Anyone using a dsb needs to be attentive to reseeding and maintaining the microfauna and critters in the bed from time to time,imo. This helps keep it a live sand bed with well channeled deeper areas fed by nutrients flowing in with the water and the critter's waste products.
They are very intersting and useful areas of the reef but need a fair amount ofattention. .
Sorry for the preceding post ; hit the wrong key.
Yes,more depth can support more denitrifying bacteria since there is more surface to colonize if you can keep it hypoxic(low oxygen, NO3) vs anoxic( no oxygen, no NO3) and insure a supply of nutrients the bacteria need.
Unfortunately ,many beds particularly after several years of accumlation of detritus ,mulm and clumping are packed tight down deep and rather sterile; others may be anoxic with evidence of hydrogen sufide generation.
Many aquariums get enough dentirfication to meet their bioload with live rock alone or live rock and a shallow bed to do the job.
Many earlier writings on sand beds ignored the fact that the denitrifying bacteria are facutative and can live with or without oxygen and gave the impression that oxygen exposure would kill them. Hence, the must be 4 inches or more rule ostensibly to keep oxygen out of certain areas. Truth is if you keep oxygen out, you'll keep other nutrients out too. If you let a little in with other nutrients ,the bacteria will use it up and move on to the NO3.
Anyone using a dsb needs to be attentive to reseeding and maintaining the microfauna and critters in the bed from time to time,imo. This helps keep it a live sand bed with well channeled deeper areas fed by nutrients flowing in with the water and the critter's waste products.
They are very intersting and useful areas of the reef but need a fair amount ofattention. .
I use fine grained sand in some of my tanks for a beachy look. An inch or a little less should be fine. However, if at some point you choose to keep certain animals like some wrasses that need sand to bury themselves in it or certain anemones, jawfish, etc, you may wan't to build up some deeper pools 3 or 4inches of sand here and there for them. Good luck.
