DSB with MUD underneath- problematic for normal DSB methodology?

[CleveYank]

Being a veteran and promoter of DSB in WELL maintained systems I think I kinda have a grasp of what's good for them and what is not.

In a refugium use of a mud sand mix is desirable since it's remote, usually smaller than the displays and harbor inhabitants of low bio-impact (cleanup crews and pods) so things should not build up on top of the mud and sand that's in there.

A sand bed in an overfed abused system will clog literally with waste and food. Sand sifters or not. This high nutrient bed as it clogs can get near -0- oxygen and the famed dead spots. Then hydrogen sulphide.

So a healthy sandbed is not pushed too hard by excessive feeding, and over population and therfore with cleanup crews, sand sifters, some stirring of your own (the don't disturb your sandbed thing is a myth) and does not clog.

Mud does not allow easy movement of sifters, does not allow even low oxygen bacteria proliferation and will/may/could in fact on the use of a large DSB in particular a display duplicate a neglected abused sandbed and lead to dead zones. It's still been debated til the cows come home as to the positive impact as far as trace and lateral line prevention if any that mud actually contributes to begin with.

On the area of a remote sump/refugium I'd use it since I can take it offline if needed. On a large DSB in the display I think the mud layer would be an expensive waste of money that would duplicate a clogged 1 inch of the DSB. The grasses would grow just fine in a regular DSB of at least 6 months of age.

I'd use the mud in remote locations, never in one that would house 200 pounds of liverock and encrusting corals etc.

Speculation ASIDE.

Two 20 gallon setups same rock density and amount same DSB depth one with 1 inch of mud with DSB above and on with just regular DSB, with exactly equal livestock and food input and water changes and support hardware. Feed it test and chart it and tell us what happens after 1 to 2 years. Running just 1 system and saying this works this is the bomb does not give a reliable result via good method.

 

[Newreeflady]

Cleve:
That was exactly my fear with the mud- dead spots in the bed, lack of movement and compaction. I'm definitely leaning away from mud at this point. But, while it sounds like we don't need the phosphate content of the mud, there may be some trace minerals in there that are very helpful to plants. Either way, I fear that the mud will cause dead spots.

Ruprecht, I still would like to talk more about the root system of seagrasses in the context of a functional nitrogen processing dsb. It is a good point that the root system will lock up the bed and not make it mobile. This may adversely affect the sand bed stirring by our stirrers, and thus create hypoxic zones higher up, and anoxic zones as well. However, if the roots produce oxygen, then maybe this offsets it?? There has to be some way people are getting these systems to work... ??

Elegance:

I was concerned, also, that the pinched mantle may have been a symptom of fast phosphate removal. It's rough, I suppose, because the gfo is so darned effective. I had used only 1/4 on the tank. There's also the possibility that they don't like high Fe. Hmmm...


All:
On the dsb: Even if we load it up with phosphate, it isn't like it's all of a sudden going to want to dump it. It's an equilibrium process. If you run gfo on a tank with an established sandbed in a system that has never seen gfo, then you should pull phosphate from the water column, and phosphate from the bed will release to reequilibrate (on some time scale that I am unaware of). The equilibrium concentration of phosphate in the bed has changed if we have removed phosphate from the water column, and the phosphate must release from sand binding sites due to this equilibrium shift.

Seems to me that in the beginning, on clean sand surface, one could easily put a lot more food in than the system, once established, will be able to handle long-term. You must have some way of exporting phosphate, as we know...

Eventually, as you continue to dump in phosphates with no exporting system, the bed will saturate with phosphates. At that point high nutrients dumped into the system should give the same result as they would in a tank without a dsb! (remember, the bed will not just dump the phosphate, it is "full", and it will have a steady state exchange with the water column, but it will not simply release phosphate from all of its binding sites. It will do this over time, as you remove phosphate from the water and shift the equilibrium.)

So, what's the problem? ... Thing is, you're used to being able to feed X quantity and not see any algae problems. All of a sudden you see algae growing and you've not changed anything. Your phosphate levels are all of a sudden high and you think that your dsb is dumping phosphates. No! You are dumping in phosphates, and the dsb is not helping you with them.

Now, the nitrogen cycle is a whole different beast. I see places where it says that you don't need an anoxic zone, just a hypoxic zone. I've seen other places where it says that you do need an anoxic zone and this is perfectly healthy. And, there are people who say that you should stir the bed, and others that say not. As to the bed removal, I'll buy that if you plan on overloading the system and need the sand as a binding medium. But, if you're exporting phosphates like you should be, then you shouldn't have to remove the bed.

I am planning on using a dsb as something complimentary to my system- it can help process nitrogen, it houses cool creatures, can be planted(?still debating that here!?), and makes some fish and inverts feel more at home. This, imo, is what it's good for. It is not a miracle bed. I still have to do water changes to add trace elements back in, and I still need a way to export nutrients from the system. I'm hoping that running carbon, a skimmer, and growing macro in the system will facilitate this. I have not had the best of luck with gfo, even starting in small doses, so it makes me a bit nervous- but, maybe I should consider it again as well.

 

[tmz]

So the "trick" to a DSB's well being,is,too limit the amount of DOC's. Posted by 3D.

The heterotrophic bacteria that perform denitrification need organic carbon along with nitrogen and phosphorous. Much more carbon than the other two.So I think the "trick is keeping just enough flow into the depths of the substrate to provide C,N,P and maintain hypoxic conditions Too much and the available oxygen will be used by the bacteria in lieu of nitrate. Too little and sulfate reduction with H2S formation occurs. These conditions can change over time with build up clogging of the channels between sand grains and clogging of the sand surface with bacterial mulm, phosphate, organics, precipitatied metals ,etc. I've kept a dsb in one of my displays for about 8 years but I have done periodic removal of small amounts of sand with replenishment of fresh live sand.
As for the mud under sand, I'd worry about anoxia in an area with high organics from the mud in terms of H2S production. Perhaps the rhizomes could channel it all well enough but I'm skeptical.

 

[Newreeflady]

Hi Tom,

I just want to clarify my understanding of the biology:

So, are you saying that the same bacteria can use either nitrogenous compounds or oxygen? Or, is it that there are competing bacteria, some which use nitrogen (and P) along with carbon and inhabit hypoxic parts of the bed, and others that use oxygen along with carbon (and P?) and inhabit the surface. If there is too much flow through the bed, you cannot have enough of a hypoxic zone to make the dsb functional in a nitrogen reducing capacity as your hypoxic functional bacteria will be diminished. If there is too little, your hypoxic bacteria starve for lack of carbon, die off, and leave you with anoxic zones where sulfates are reduced to sulfides (by some other bactaria?), which are toxic.

Should one really have to remove parts of the bed if the dsb is functioning properly? Does its becoming saturated in phosphates somehow act as a dsb clogging glue, binding grains of sand together? Or, is it simply impossible to keep the number and diversity of sand sifters necessary to keep the bed moving and sufficiently oxygenated to prevent anoxic zones from forming? In that case, the dsb is not self-sufficient, but can be forced to be functional with a small amount of maintenance stirring (as suggested by Cleve.) Still, I can't see why you'd need to remove parts of the bed unless you somehow neglected this stirring, or unless you are using the bed for something it wasn't meant for (such as binding phosphates irreversibly.)

While I think we've abandoned the mud discussion (I'm not going to put it in after consideration of the points in this thread), I am finding this to be a really helpful conversation and thank you all for contributing!

Mind if I ask one more question? Where does rock fit in here? If rock is buried, does that cause more dead spots to occur? Should it matter? I mean if we have trouble with rock-sand interface, shouldn't we see more dead spots at the sand-glass interface as well? And, if so, wouldn't that preclude functional dsbs in smaller systems (with more sand-glass interface per volume sand)?


-A

 

[ruprecht]

In most tanks there is usually more DOC/P than what is on a nutrient rich reef,let alone one that's limited.I don't think that limitation of DOC/P is the case with DSB's.

I was addressing your 'macro' issue. If a hobbyist can't keep their system in balance, that is their fault and shouldn't be included in the conversation. A balanced system with a healthy DSB will not have nutrient build up nor will fail in a few years.

I will continue to follow the conversation out of curiosity but I can't continue to discuss what happens when your example system is improperly maintained.

NewReefLady:

As 3D pointed out the seagrass O2 influence near rhizomes appears to be highly localized and negligible. However, a low flow severely impairs the functionality of a DSB. Seagrass may be a great addition to your tank and keeping the flora with the fauna may present a worthy challenge. I for one would not encourage the use of seagrasses in your DSB if the sand is to be relied upon as your major biological filtration system.

 

[tmz]

Hi Angela
The bacteria that perform denitrification are faculative hetertrophs.

As heterotrophs they need organic carbon(sugars, etc) since they can't produce it as photosynthetic( autotrophic bacteria ) can. They need phosphorous and nitrogen for food as well.

Faculative means they can breathe (use oxygen for energy) both in the presence of oxygen or they can take it from NO3 when there is no oxygen. Taking the oxygen directly is more rewarding for them so they will respire aerobicly when oxygen is avaialbe and switch to NO3 reducing ,(anaerobic respiration) when its' not. When the nitrate is gone you have anoxia( < 0 ORP) and SO4 reducing bacteria dominate producing toxic H2s( hydrogen sufide) as a by product.
So if organics get down into the bed and an adequate flow to maintain hypoxia is not maintained; trouble ensues as anoxic conditions with available food encourage SO4 reducing bacteria that take their oxygen from the SO4.
Due to the closed system nature of a reef tank a deep bed is likely to develop anoxic areas over time unless it is kept alive with benthic fauna to channel and burrow it or some alternative force beyond diffusion to move water down into the bed.
I don't think PO4 is the only conern. I think bacterial mulm, detrius, precipitated metals and other things can acculate in/on old sand over a period of years.
When you bury a rock in the sand , you are burying the organics on the rock , providing bacteria food to a likely anoxic area which can encourage SO4 reduction and hydrogen sulfide formation which is often evident in black sulfide deposits on buried portions of live rock.I set my rock up on palstic or pvc pillars to let it rest on top of the sand.

 

[skanderson]

no deep insights on how well this will work out but just a thought. i would thing about placing a sheet of enkamat or a similar barrier down over the mud before placing the dsb. that way the roots could grow through but large scale disturbances that would lead to cloudy water might be avoided. this sounds like a cool experiment and i hope you set up the system and keep us informed on how things go.

 

[Newreeflady]

Hi Angela
The bacteria that perform denitrification are faculative hetertrophs.

As heterotrophs they need organic carbon(sugars, etc) since they can't produce it as photosynthetic( autotrophic bacteria ) can. They need phosphorous and nitrogen for food as well.

Faculative means they can breathe (use oxygen for energy) both in the presence of oxygen or they can take it from NO3 when there is no oxygen. Taking the oxygen directly is more rewarding for them so they will respire aerobicly when oxygen is avaialbe and switch to NO3 reducing ,(anaerobic respiration) when its' not. When the nitrate is gone you have anoxia( < 0 ORP) and SO4 reducing bacteria dominate producing toxic H2s( hydrogen sufide) as a by product.
So if organics get down into the bed and an adequate flow to maintain hypoxia is not maintained; trouble ensues as anoxic conditions with available food encourage SO4 reducing bacteria that take their oxygen from the SO4.
Due to the closed system nature of a reef tank a deep bed is likely to develop anoxic areas over time unless it is kept alive with benthic fauna to channel and burrow it or some alternative force beyond diffusion to move water down into the bed.
I don't think PO4 is the only conern. I think bacterial mulm, detrius, precipitated metals and other things can acculate in/on old sand over a period of years.
When you bury a rock in the sand , you are burying the organics on the rock , providing bacteria food to a likely anoxic area which can encourage SO4 reduction and hydrogen sulfide formation which is often evident in black sulfide deposits on buried portions of live rock.I set my rock up on palstic or pvc pillars to let it rest on top of the sand.

Hi Tom, super helpful info! I did not realize the bacteria in the hypoxic and aerobic layers were one and the same! Sounds like the sulfate reducing bacteria are different, though. Interesting.

That makes sense with additional things accumulating in the bed, perhaps impeding the flow through the bed and the burrowing creatures from burrowing there as well. Maybe it does make sense, then, to replace the bed in parts. Can one remediate the removed sand, by bleaching perhaps?

What if you bury base rock, rock that was land mined and is dead. Do you have to worry, then, about dead spots at the rock interface? I gather since you didn't mention it that the glass sand interface is not a concern as a "dead spot"? Also, with pvc pipe, I was talking about that in another thread. I'm wondering about sand or water in the actual pvc pipe, doesn't that become a dead area? Should we lay cement in there, maybe?

Thanks!

Ruprecht, I think that the seagrasses sound really cool, but am quite concerned about impeding flow via root compaction. I don't want that under-area to become a wasteland. Still a bit conflicted on the whole planting thing.

Thanks again all!
-A

 

[tmz]

Typically, the pvc supports are cut in half lengthwise to avoid encased areas or drilled full of large holes.

Any material free of organics or precipitants could be buried even rock. I'd be careful about what might be in any rock that might leach out if localized ph varied under the sand. Also , if ph drops down in the sand due to some anoxic area acid buildup or bacterial activity it could dissolve some of the rock.
If it's dry base rock it may still hold organics which can be removed with bleach or precipitants such as metals or phosphate which can be removed with an acid bath( vinegar or muriatic acid). Used aragonite( reef sand) can be treated the same way but the acid bath melts the surface ,dissolving the calcium carbonate and releasing it and whatever is sunk in it like copper and phosphate for example. With some sand what you have left may not be worth the effort .

There might be less than adequate flow at the glass /sand interface to support oxic or hypoxic areas at some depth but the glass has no organics on/in it like live rock does so the risk for H2S producing activity there is lower.

I'm not sure about the SO4 reducing bacteria. I did believe they were the same faculative heterotrophs but another reefer whom I respect suggested they were a different type ie obligate heterotrophs which must have anoxic conditions to thrive. Have to do some research on it.

 

[3D-Reef]

I was addressing your 'macro' issue. If a hobbyist can't keep their system in balance, that is their fault and shouldn't be included in the conversation. A balanced system with a healthy DSB will not have nutrient build up nor will fail in a few years.
I will continue to follow the conversation out of curiosity but I can't continue to discuss what happens when your example system is improperly maintained.

I realize that My example useing micro-macro too explain the process was as clear as mud:lol2:,and I apologize for any confusion it may have caused.But at work today I thought of a better example.So if you would bear with Me one last time,I'll try again to restate My position.

For discussion,example,...
Let's say that an average person,with a healthly life style,needs 2000 calories per day.He niether gains weight or loses weight.ie a healthy DSB
Compare that too a couch patato,with a low metabolizim who eat's 2000 calories day.Because of the low metabolizim he only needs 1000,but since he eats 2000cal's/day ,a 1000 calories,/day,is going into storage.ie an over fed DSB
Now compare those two,too a marathon runner.If the runner is only eating 2000 cal's a day,and he's burning up 3000 cal's per day,he is useing 1000 cal's from storage,and if he is to survive long term he has to come up with another 1000 cal's from some where.ie SGDSB

Much like the runner,seagrass beds are at a higher metabolizim.Although the sand will provide 2000cal's of nutrition (by the use of hetrotrophic bacteria),the grass has to come up with the other 1000cal's some where or use up their reserves from storage.This is where the nitrogen-fixing,cyanobacteria (actinomycetes,and mycorrhiza) come into play.These bacteria supply up to 50% of the plants DIN needs.

In order for the plants to up-take DIN,the prefered being ammonium,they have to use "glutamine from glutamate and ammonium ,catalyzed by glutamine synthetase.This requires energy (1 ATP is needed for each glutamine synthesized)."*
To take up N03,unlike algae,they first have to demineralize it to ammonium by the use of two enzymes.(nitrite reductase,nitrate reductase) Once it has been demineralized to ammonium and up-taken by glutamine and ATP, it can then be assimilated into ammino acids for storage/growth.

As 3D pointed out the seagrass O2 influence near rhizomes appears to be highly localized and negligible. However, a low flow severely impairs the functionality of a DSB. Seagrass may be a great addition to your tank and keeping the flora with the fauna may present a worthy challenge. I for one would not encourage the use of seagrasses in your DSB if the sand is to be relied upon as your major biological filtration system.

The 02 influence may be localized,but IMO,with 80% of the total bio-mass being below the sand surface,it can have an influence that is worthy of mentioning.(see attached photo)

IMO having seagrasses,even with the high motabolizim,does not mean you can forgo good general husbandry.ie water changes,skimmers,ect..

CleveYank "The grasses would grow just fine in a regular DSB of at least 6 months of age."

IME It takes at least 8-12 months for grass (turtlegrass) to become established,with 10 lbs of mud too 400lbs of sand.IMO with out the mud getting the bacteria to become established,your looking at at least 12 months.

IME I had a SMB set up for longer than 8yrs and when I took it down last year,it wasn't any more compacted than the day after I put it in.

*Seagrasses,2006