Deep Sand Bed -- Anatomy & Terminology

[tastydog]

Yes. Any sand sifting anything is bad for a DSB. They feed on the organisims in the top layer of sand which are a very important part of the process of breaking down detrius.

There are arguments to this and there is no quotable scientific test on this. However, once you see how much those sand sifters move, and knowing they need a lot of food to survive in captivity means they are destroying organisms in the top layer of sand in mass quantity.

You decide if it is worth it, to each their own. (They also do a great cleaning and stirring job.)

Brandon

 

[Aquarist007]

Buried live rock means buried organic material on/in the rock. This provides food for heterotrophic bacteria that will exhaust the O2 and NO3 in the water around and in the rock pores , likely leading to an anoxic condition at some point. Then sulfate reducing bacteria will begin to respire O2 from the sulfate in the water and produce toxic hydrogen sulfide as a by product.
I prefer to set the rock up on plastic feet being careful to keep the space under the rock as open as possible to avoid blocking flow under the and then backfill with sand.

Hi Tom
I have always thought that the area between the sandbed and live rock was a very important anoxic area for denitrifying bacteria. Would you not remove a vital area for those bacteria if you put the rock up on plastic feet and allowing oxygen to reach that area?

 

[Aquarist007]

I have 40lbs of live sand in my 29G Oceanic Biocube. ive been told by some people that it is too much and told by others that it is fine. I have about 2 inches in the deepest parts. Any comments or suggestions would be great. If this is too much I think I can still remove some sand as it has only been in my tank for just under a month.

It should not be a problem but if cyano develops and remains a nuisance then you might want to consider adding a small nano power head to create more flow across the surface

 

[tmz]

Hi Tom
I have always thought that the area between the sandbed and live rock was a very important anoxic area for denitrifying bacteria. Would you not remove a vital area for those bacteria if you put the rock up on plastic feet and allowing oxygen to reach that area?

Hi

Denitrification occurs in the sand and in or on the rock in hypoxic(low oxygen) a not anoxic(0 oxygen ) areas. Depth of sand past an inch or so doesn't matter much. It even occurs in bacterial mulm.

The rock should be on the sand ;not hanging over it ,with supports buried in the sand to prevent tumbling from unforseen excavations. The supports should not be such that they would impede flow through the sand.

The rock on the sand also helps advective flow into the sand since as an obstruction it reduces water pressure under the rock causing an up wellling of water and consequent downflow. So the flow under the rock should actually be higher than the surrounding sand bed.
Anoxic areas are undesireable since they are void of oxygen and nitrate and lead to sulfate reducing bacteria taking over . Toxic hydrogen sulfide gas is a by product of sufate reduction.
Burrying rock amounts to burrying bacteria food . The organic material on/in buried rock will die and rot providing organic carbon for bacteria to feast on With the relatively low water flow in the sand , the oxygen will deplete and then the nitrate will go to zero in the area leading to an anoxic condition.

I agree the 2 inches of sand should be fine . I'd use it .If it becomes a problem later it can be siphoned out incrementaly.

 

[Aquarist007]

Hi

The rock should be on the sand ;not hanging over it ,with supports buried in the sand to prevent tumbling from unforseen excavations. The supports should not be such that they would impede flow through the sand.

.

Thanks --this clarifies my original understanding and thanks for the detailed answer

 

[tigerjace]

great article and very helpful. I've used sand beds in my reef tank and it works! In a healthy aquarium, you almost don't need to do water changes. I've gone 2yrs without a water change!!

 

[tmz]

Water changes are a source of replenishment for important elements as well as the export of nasties. IMO and E frequent changes are a big plus.

 

[Whys]

great article and very helpful. I've used sand beds in my reef tank and it works! In a healthy aquarium, you almost don't need to do water changes. I've gone 2yrs without a water change!!

I don't recommend that. Water changes aren't only used to keep the water clean, but to replenish calcium and magnesium, as well as important trace elements that we don't normally measure for. Water changes are always important, even in a clean tank with a healthy DSB.

 

[Sisterlimonpot]

Welcome back whys.

 

[Aquarist007]

Welcome back whys.

welcome back Whys and Sisterlimonpot:bounce3::bounce3:

 

[GT3]

Hi

Denitrification occurs in the sand and in or on the rock in hypoxic(low oxygen) a not anoxic(0 oxygen ) areas. Depth of sand past an inch or so doesn't matter much. It even occurs in bacterial mulm.

The rock should be on the sand ;not hanging over it ,with supports buried in the sand to prevent tumbling from unforseen excavations. The supports should not be such that they would impede flow through the sand.

The rock on the sand also helps advective flow into the sand since as an obstruction it reduces water pressure under the rock causing an up wellling of water and consequent downflow. So the flow under the rock should actually be higher than the surrounding sand bed.
Anoxic areas are undesireable since they are void of oxygen and nitrate and lead to sulfate reducing bacteria taking over . Toxic hydrogen sulfide gas is a by product of sufate reduction.
Burrying rock amounts to burrying bacteria food . The organic material on/in buried rock will die and rot providing organic carbon for bacteria to feast on With the relatively low water flow in the sand , the oxygen will deplete and then the nitrate will go to zero in the area leading to an anoxic condition.

I agree the 2 inches of sand should be fine . I'd use it .If it becomes a problem later it can be siphoned out incrementaly.

Sorry but I'd like to correct you, so everyone can benefit. I'm a environmental science major, ocean represents one of most important part on our planet.

Firstly, denitrifying bacteria only lives in anoxic area, it is a desirable area for them unlike hypoxic area where nitrifying bacteria can thrive, whereas denitrifying bacteria cannot.

1-2 inches under sea floor(or in aquarium the sand bed), is not considered as hypoxic zone. There is still a great amount of oxygen and water circulation for nitrifying bacteria to live in.

Therefore burying a rock under 2 inches will not help denitrifying bacteria to grow, as the depth is not near to anoxic zone also the rock is porous.

If nitrifying bacteria grows in a specific zone, you will never find denitrifying bacteria in the same zone.

To enter hypoxic zone, you will need over 2 inches of sand, and for anoxic zone you need over 4 inches of sand to stimulate a mini ocean.

If you were to manage to keep denitrifying bacteria under an impermeable rock, they are not going to thrive long enough to complete the cycle and for such a small area it is not going to give you benefit also.

 

[Paul B]

I'm a environmental science major, ocean represents one of most important part on our planet.

Although I agree with almost everything you say, I do disagree just a little.
I am not an envirnmental science major or any other type of major and I know you are well versed on the subject, probably much more than I am but I have been collecting in tide pools for the better part of fifty years and have also had an aquarium for almost 60 years and I have an observation.
I practically grew up in a tide pool.
When I collect in a tide pool, almost any rock I lift off the fine sand or muddy bottom is full of hydrogen sulfide, even if that rock is not burried at all in the bottom. It just needs to be on the bottom enough to contact it on all sides.
This happens very fast because if I leave that rock over for a few days then place it back on the bottom, it will again form hydrogen sulfide by the next tide. I think if you place a rock in an aquarium that is kind of flat and your substrait is fine enough it too will produce an anoxic or at least oxygen limited area.
An aquarium is not like the sea where we have tides, storms and waves. Our tanks remain kind of static. My reef is very old and sometimes rocks go years before I move them, these areas in "my" tank do not go anoxic because I use gravel but with sand that acumulates detritus even faster than the sea due to a lack of the above mentioned water movement I believe there will be areas with such a limited amount of oxygen that anerobic bacteria will thrive. I find this in my local NY tank. It uses beach sand and mud from the Long Island Sound. If a rock is stuck to the bottom for a few weeks and I allow detritus to build up as I usually due because there is no filtration in that tank, I will get hydrogen sulfide.
So it is my un educated opinion that in a tank in certain circumstances when the sand is fine enough and the rock is un porous enough you can have limited areas of oxygen.
Of course this is just "my" opinion and I am not the God of anerobic bacteria. :dance:

 

[tmz]

Sorry but I'd like to correct you, so everyone can benefit. I'm a environmental science major, ocean represents one of most important part on our planet.

Firstly, denitrifying bacteria only lives in anoxic area, it is a desirable area for them unlike hypoxic area where nitrifying bacteria can thrive, whereas denitrifying bacteria cannot.

1-2 inches under sea floor(or in aquarium the sand bed), is not considered as hypoxic zone. There is still a great amount of oxygen and water circulation for nitrifying bacteria to live in.

Therefore burying a rock under 2 inches will not help denitrifying bacteria to grow, as the depth is not near to anoxic zone also the rock is porous.

If nitrifying bacteria grows in a specific zone, you will never find denitrifying bacteria in the same zone.

oTo enter hypoxic zone, you will need over 2 inches of sand, and for anoxic zne you need over 4 inches of sand to stimulate a mini ocean.

If you were to manage to keep denitrifying bacteria under an impermeable rock, they are not going to thrive long enough to complete the cycle and for such a small area it is not going to give you benefit also.

Well, I wish you had asked a question rather than posting infromation that demonstrates a misunderstanding of the nitrogen and anaerobic and aerobic activity.

Ufortunately, your post needs to be corrected:

Firstly, denitrifying bacteria only lives in anoxic area, it is a desirable area for them unlike hypoxic area where nitrifying bacteria can thrive, whereas denitrifying bacteria cannot.

False.

Denitrifying bacteria are faculative heterotrophic bacteria. Heterotrophic means they can't produce their own carbon sources . Faculative means they use oxygen directly and when it's not available as in hypoxic conditions go to NO3( nitrate ) for oxygen to respire. they live in the presence of oxygen and in hypoxic areas too. They do not live in anoxic areas where no oxygen or nitrate is available. Anoxic areas are the domain of sulfur reducing bacteria which take oxygen from sulfate(SO4),creating toxic hydrogen sulfide gas and sufides as by products.


Therefore burying a rock under 2 inches will not help denitrifying bacteria to grow, as the depth is not near to anoxic zone also the rock is porous.
Two inches of sand is plenty of depth for anoxia.

False,

Burying a live rock a couple of inches down in the sand will provide decaying organic matter which provides the organic carbon the heterotrophs need to flourish. They will exhaust the oxygen and nitrate creating an anoxic environment where the sulfur reducing bacteria will take over .This is why buried areas of rock often show black sufide deposits which occur as hydrogen sulfide is oxidized.


If nitrifying bacteria grows in a specific zone, you will never find denitrifying bacteria in the same zone.


False,

As noted above denitrifying bacteria are faculative heterotrphs which means they live in oxic( high oxygen) and hypoxic (low oxygen including that in NO3)areas often even in the same clump of bacterial mulm if a source of organic carbon is present.

oTo enter hypoxic zone, you will need over 2 inches of sand, and for anoxic zne you need over 4 inches of sand to stimulate a mini ocean.


False.

Studies have shown that denitrification occurs quite well in shallow sand beds of an inch or less.

If you were to manage to keep denitrifying bacteria under an impermeable rock, they are not going to thrive long enough to complete the cycle and for such a small area it is not going to give you benefit also.[/QUOTE]


False.

Live rock is not impermeable. The faculative heterotrophs live in the rock and the sand under it. As flowing water strikes the rock or any obstruction there is a drop in water pressure under the rock footprint which causes advective flow, an upwelling under the rock and consequent downward flow of water to the void created by the upwelling water.. This flow sources organic carbon ,oxygen and nitrate and mitigates against anoxia. This is part of how natural reefs work as sediment nutrients flow upward through the reef structure.

Good luck in your studies. Reading about the nitrogen cycle, nitrifying and bacteria, heterotrophic bacteria , advective flow , anaerobic digestion,and basic reef chemistry will be helpful in improving an understanding of the interplay between the physics, chemistry and biology of natural reefs. Searches on these terms will yeild a welath ofinformation and many associated scientifc studies.

 

[Paul B]

Also wander around in a muddy tide pool for a while and pick up a bunch of rocks.
It's fun also :lmao:

It's amazing how much you can learn by lifting rocks, that is why it is one of my favorite pasttimes. The pool where I collect has muddy and sandy areas.
The sandy areas are no problem you can lift rocks all day and not find hydrogen sulfide but the muddy areas host the most variety and number of life forms "as long" as there is some slight flow of water. As soon as the areas around the rock fill in with mud, the creatures must leave because it forms hydrogen sulfide very quickly and nothing visable lives there. You can immediately tell because it is jet black and stinks.
These rocks do not have to be burried at all, they just need to be flat and in contact with the mud.

 

[tmz]

Hey Paul, I'm scared of the Long Island Sound mud and sand. I was bitten once by one of those green sand worms as we were collecting them for bait somewhere near Port Jefferson. The mud if it's fine grained enough could probably house anoxic areas very close to the surface since flow through it would be negligalbe btw.

 

[Paul B]

You are not supposed to pick them up so they can bite you, you need to pick them up like a snake just behind the head. They got some big fangs.
Make great fish food though.
As for mud, in the pool I collect there is a place I call horseshoe crab city because it sometimes is just loaded with tiny 3/16" horseshow crabs. It is perfect for them because the mud is so fine there that they can plow through the fine mud. They have problems with regular mud and forget sand which is much too coarse for them.
If you step there you sink up to your knees in ooze and lose whatever shoes you are wearing.
50 yards from them is fiddler crab city, I don't have to explain that but that area is just above low tide sea level and it is sand.
In the shallow water there are hermit crabs. They disappeared for a dozen years but happily, now they are back.

 

[Aquarist007]

Exactly what I was going to post Tom:lol:
When I read that post I was wondering how long it was going to take before the op was straigtened out
Good stuff I am amazed at how much I learn everyday in this hobby:thumbsup:

 

[tmz]

deep sand is great.

Not much information there.

Deep sand can be useful for sand critters which live in it and or fish like some wrasses and jawfish that burry in it to rest and hide or other creatures that need it like some anemones, pistol shrimp,etc. It can also help denitrification if it is live and well burrowed or an alternate means of flow through it such as advection to a degree to deliver nutrients including nitrate, phosphorous and organic carbon is in play.
It is not necessary for denitrification in a reef tank,however. Some find it aesthetically pleasing; some don't. Without periodic maintenance including replenishment with live sand from time to time, deep beds will clog over time,in my experience, and source sulfate reducing bacteria which produces toxic hydrogen sulfide gas as well as the release of toxins that may build up in it..

 

[tmz]

Exactly what I was going to post Tom:lol:
When I read that post I was wondering how long it was going to take before the op was straigtened out
Good stuff I am amazed at how much I learn everyday in this hobby:thumbsup:

Thanks

There's nothing in my last post that wasn't said elsewhere in this monster thread.probably by me at least twice already. I wasn't going to respond at all, hoping someone else would but the information was just wrong and ultimately I felt a response was needed even if it's repeat information.

 

[Paul B]

deep sand is great.

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