With or Without Plenum?

[mikey98]

I am starting a 55 gallon reef tank and want to know if I should use a plenum or not. I have a skimmer and sump that is much bigger that what I need for my 55. I also have a Sea Storm that is not hooked up that I could hook up. Please let me know your opinions.

Thanks

Michael

 

[Roach]

I think nowadays that it's more of a personal preference. I have heard many people swear by them and others say that they would never use something they didn't really need. With today's skimmers I think the plenum is kinda dieing out. I have never used one and my tanks seem to do fine. I like going with the DSB and strong protein skimming approach. If you want to do one I don't think it could really hurt anything.

 

[KanUCme]

Just go with the DSB and LR, with a good skimmer mike.
-Nick

 

[Minh Nguyen]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by mikey98:
<strong>Would it hurt to have one? They are easy and inexpensive so I figure that if it won’t hurt and can only help then why not. What do you think?

</strong><hr></blockquote>
A DSB work just as well if not better than Plenum. There are several reasons why I would not use it:
1. Take the trouble setting it up
2. Empty space under the sand that serves no purpose. I have no good explanation why it is need, and why it would help the denitrification process. I have certainly looked into it several years ago. This space would be better serve if we have sand in it> a deep sand bed.
3. If some how the space is compromise because animal digging or power head blowing, the whole plenum would not work because O2 would get to the bottom of the plenum
4. For compatible function, plenum needs to be much deeper than a DSB. If you reed original information/paper, the size of the gravel recommended is very coarse and very deep gravel bed (10+ inches). I don’t have this paper anymore but that was what I remember from reading it in 1998.

It was though that if the sand bed gets “too anaerobic” harmful gas might form and cause harm to the tank animals. That was why plenum was put in place, to keep the sand bed from getting to anaerobic. We now know that this is not true, therefore, plenum is not needed. It can only impeded the function of the sand bed.

[ February 06, 2002: Message edited by: Minh Nguyen ]</p>

 

[[email protected]]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> A DSB work just as well if not better than Plenum. There are several reasons why I would not use it:
1. Take the trouble setting it up
2. Empty space under the sand that serves no purpose. I have no good explanation why it is need, and why it would help the denitrification process. I have certainly looked into it several years ago. This space would be better serve if we have sand in it> a deep sand bed.
3. If some how the space is compromise because animal digging or power head blowing, the whole plenum would not work because O2 would get to the bottom of the plenum
4. For compatible function, plenum needs to be much deeper than a DSB. If you reed original information/paper, the size of the gravel recommended is very coarse and very deep gravel bed (10+ inches). I don’t have this paper anymore but that was what I remember from reading it in 1998.
It was though that if the sand bed gets “too anaerobic” harmful gas might form and cause harm to the tank animals. That was why plenum was put in place, to keep the sand bed from getting to anaerobic. We now know that this is not true, therefore, plenum is not needed. It can only impeded the function of the sand bed.
<hr></blockquote>

I'd have to disagree with most of this information. Personally I feel a big reason why most people prefer a DSB over a plenum is your #1 reason, the trouble of setting one up. It's obviously much easier to just dump inches full of live sand on the bottom of your tank rather than properly construct and follow a plenum methodology. That doesn't necessarily mean it's better, just easier.
In your second statement you state that the plenum serves no purpose other than taking away space from what could be part of a DSB. The purpose of the plenum area is to provide a pocket of water with LOW SURFACE AREA under the sand bed. The low surface area, created by the lack of a substrate prevents growth of excess orgranic life, including aerobic and anaerobic bacteria along with other micro-organisms that can live in an oxygen deprived enviournment. By design, this keeps the plenum space from going completely anoxic and keeps the O2 levels around 1ppm. If this area was of a high surface area, the O2 levels would almost certainly fall to or very close to 0ppm. In contrast, a DSB's lower layers become much more anoxic than a comparable plenum based system.
In your third statement you loosely claim that in a disaster situation, a plenum system would crash because of O2 entering the plenum area. This is a fairly absurd point to make since a DSB system would be even more severely compromised in the exact same circumstances. The very principle of how and why a DSB operates revolves around the metabolization of organic compounds. The lower levels of a DSB being very anoxic would contain large amounts of partially metabolized gases, and would be extemely dangerous to all tank inhabitants should they be disturbed and bubbled up.
Also you mention that the plenum is compromised by animals digging into the gravel layers. A properly setup plenum recommends a layer of screen two inches below the top layer of gravel. This prevents burrowing inhabitants from disturbing the lower levels of gravel. A DSB system in comparison strongly discourages the use of any animals that could/would disturb the sand bed. The only real problem I have heard of regarding this matter is a few people have claimed that their plenum systems have crashed because the screen became choked by small organisms. I've never experienced this problem myself, and it could be possible that a courser mesh screen along with better detritus removal would have prevented this from happening.
Your fourth point seems very odd. Most of the readings I've come across recommend a plenum height of 1 to 2 inches, along with 4 to 5 inches of gravel on top. This gives us a total height of 5 to 7 inches. Every plenum I've setup has been around 5 1/2 to 6 inches and nitrates have always been 0ppm.
My main problem with a DSB is it's an energy based system. It requires a huge bioload to operate correctly to do the same job of a comparable plenum. A DSB relies on millions of various sized organisms within the sand bed consuming, metabolizing and releasing energy in various forms. The continuous release of detritus over the top of the sand bed is considered good in a DSB as it is the food for the biological food chain. The detritus feeds the appetite of the huge bioload within the bed. All of this detritus and life that consumes it is essentially nothing more than organic energy for the carbon system. This energy based system relies on metabolizing orgranic compounds into gases to remove them from the system. Another inherant problem with this is that organic phosphorous tends to accumulate from all of the detritus and waste within the sand bed. As an energy based system requires gases to be metabolized, the phosphorous is never removed from the system as it simply does exist in a gaseous form.
A plenum system can be kept much cleaner as it does not require its sand bed to be kept undisturbed. This allows higher water flow over and around the sand bed, which can keep detritus in the water column where it can be removed by mechanical filtration. A plenum system can also make use of more aggressive sand stirrers and sifters such as cucumbers and gobies. They continuously stir up the upper sand layer, helping to lift up the detritus into the water column.
You must remember that the plenum's sand bed needs to be kept fairly exposed to function properly. If you set your live rock directly on top of the sand bed, you are choking off areas and diffusion will not take place there. Most experts recommend keeping at least 75% of the gravel bed open. This can be done in various ways, such as keeping as small a footprint of live rock on the sand bed as possible, or even elevating the live rocks with acrylic rods. I prefer to put the plenum in my sump myself. This allows it to have a 100% open area, and allows you to use much higher water flow over the bottom of the tank. It also allows you about 6 inches of tank space that is no longer required for a plenum/sand bed. In my tanks I run an overflow into another similiarly sized tank, which serves as a plenum sump. The water is mechanically prefiltered on the overflow and also into some filter floss before it enters the sump. The sump has its own circulation pump, space for a heater, and any other equipment such as protein skimmers, probes or chillers. The return pump is also in the tank returning the water to the main tank. All of the powerheads and water pumps in the plenum sump are positioned within an eggcrate housing I made to prevent them from moving and preventing any disaster scenarious such as a powerhead's suction cups giving way and launching itself into your sand bed. A sump plenum also does not require a layer of screen below the top layer of live sand because nothing will ever be burrowing into it. This can rest the minds of those people who think the sky will eventually fall on them with a plenum. Although, as I stated above, a courser screen will do the same thing in tank.

By using strong water flow within the main tank, detritus is practically non-exsistant as it gets caught in the prefilter sponge and filter floss which gets rinsed/replaced daily. This allows the detritus to be removed from the system rather than it being broken down and added to the carbon energy system. Is a plenum or DSB perfect, no. Anybody could crash any system with improper implementation or preventitive maintenance. I just tend to prefer keeping my organics in check, keeping the tank bioload lower, which keeps the ORP higher, leading to higher quality water and a more stable system. I don't expect you to find much agreement with me on this or any forum, it's been very trendy the last few years to abandon plenums and go with a DSB and threads on any reef forum will attest to that fact. I suggest reading up as much as you can on the matter, and not taking the word of anyone, including myself in a messageboard as final, just another opinion on what you base your decision. My personal reasons for a plenum over a DSB are obvious, but others will firmly argue that everything I said MUST be BS because they have been running a DSB and they're not having any problems, so their method is the best. To each their own, this is just my personal and completely biased opinion on this highly debated topic.

 

[Minh Nguyen]

cwills,
The premise that is all-important in your argument is that anoxic condition can cause the formation and release of gases or other substances that are deadly to the tank inhabitants. The plenum space prevents the bottom layer from being anoxic thus prevent the formation and release of these gases. IME, and given the fact that many, many tank do just fine with a very deep sand bed, this premise is false. Plenum is not needed due to the fact that the premise that is essential to it creation is false.

Also consider the following points:

The rate of the concentration of O2 decrease as the function of the dept of the sand bed depends on many factors. These factors included but not limited to the size of the sand, the number of organisms that is in it, the concentration of the O2 at the surface of the sand, the water movements above the sand, the temperature and many other factors.

If your important premise is true, the plenum of each system need to be different or else, one can crashed the tank if the concentration of O2 somewhere in the plenum system reaches anoxic condition.

I search literature regarding sand bed with and without plenum extensively before deciding that plenum is not needed. At this time, I have a 10+ inches deep sand bed consists of very fine sand. Certainly I have many diggers in my critter population in my tank. There is no, and never was any risk in deadly gas release to poison my tank.
I NEVER ONCE SAID THAT PLENUM DOES NOT WORK NOR WILL CAUSE TANK CRASH IF PLENUM SPACE IS SOME HOW COMPROMISED. I only said that plenum is not need, and that if you use the same amount of sand, a plain sand bed will work just as well if not better than a plenum system. If somehow, the plenum space was compromised, the plenum just would not work to lower nitrates, but it won’t crash your tank. In a DSB, if a fish digs deep, it will not compromise the entire sand bed. There are plenty other areas that are anaerobic in the rest of the sand bed.

Your argument that DSB requires more fauna to work is wrong. You completely misunderstand how DSB works. DSB, like plenum, uses bacterial to break down ammonia/nitrates back to N2 in anaerobic conditions. The fauna is NOT what breakdown ammonia to N2. I feel that diversity is important, and larvae produces by fauna are food for the fish and coral, so I try to maximize the diversity and density of live in the sand bed. I believe that the minimal fauna required for functioning DSB and plenum is the same. Both methods need just enough fauna to prevent clumping of the sand. This is similar in both methods because the cause and the prevention is the same.
Regarding the dept of the plenum system, if you find the translation of the original writing by Dr. Jaubert, you find that he recommend very coarse graves and a very deep gravel bed. You don’t have to tank my word for it, just spend the time to do the search and you will find what I said is true.

I am tire of typing. Please note that I sand plenum will works in lower nitrates. I just think that it does not offer any advantage over a simple sand bed, and that it has potential to not work if poorly built. DSB is much easier to do and have no potential for failure.

 

[mikey98]

Would it hurt to have one? They are easy and inexpensive so I figure that if it won’t hurt and can only help then why not. What do you think?

 

[fishpoo]

if you go with a plenum, your sandbed life will be limited due to the larger size particles of the aragonite bed. With a fine sand bed, worms and bugs can multiply faster and easier.
Also, as one who tried both, if the plenum bed starts growing caulerpa and you wish to pull it out, some of the bed will come with it. The fine sand would be less of a disturbance.

 

[Anonymous]

When I set up my tank several years ago, I could find no compelling reason to use one, but several reasons not to: more work, more potential for problems, you get great resluts without one, and most people don't use them.

RR

 

[mikey98]

WOW! Lots of big words and talk. Can anyone speak English to me? I am new you know. It sounds to me that it is a matter of personal preference. Both work much the same way and do the same thing. Both require the proper setup and both have their pitfalls. Well I guess it could come down to a toss of a coin.

Thanks for the words,

Michael

 

[[email protected]]

Minh,

You may want to re-read my first post. You state that the "all-important" premise in my arguement is the fact that a DSB creates anaerobic zones which are dangerous. While I beleive this can be true, and can also be true of a plenum, I did state that my main problem with a DSB is it's an energy based system. As far as anaerobic zones within a DSB or plenum bed, a plenum's design does reduce the risk of a bed becomming completely anerobic. The small grain size and depth of a DSB cannot claim this. I am not trying to say that under normal circumstances a DSB is dangerous, but I'll give more on that later.

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>...At this time, I have a 10+ inches deep sand bed consists of very fine sand. Certainly I have many diggers in my critter population in my tank. There is no, and never was any risk in deadly gas release to poison my tank....

In a DSB, if a fish digs deep, it will not compromise the entire sand bed. There are plenty other areas that are anaerobic in the rest of the sand bed.
<hr></blockquote>

I certainly hope that your diggers and fish do not dig too deep, because you may be in for a shock if they do. A DSB can(read "can", not necessarily "does") contain partially metabolized gases. I wouldn't want to take a chance of finding some and crashing the tank if I were you. This rolls me right into my next point...

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote

Your argument that DSB requires more fauna to work is wrong. You completely misunderstand how DSB works. DSB, like plenum, uses bacterial to break down ammonia/nitrates back to N2 in anaerobic conditions.

I am well aware of the nitrogen and carbon cycle, but a DSB CERTAINLY DOES require much more fauna to "work" than a plenum. A plenum can work with bacteria alone. The larger grain size of the substrate can in and of itself prevent sand clumping, providing that kalkwasser isn't being introduced to the point of ridiculous supersaturation. Plenum systems can and do work just as well in freshwater tanks, where absolutely no digging critters are introduced into the bed. A plenum can nitrify/denitrify with bacteria alone. A DSB uses the same bacteria to do its job, but the fauna must be there to prevent clumping. The fine sugar sand that a DSB uses necessitates the use of these animals. I'm sure you already know this information, but if you don't take my word for it, here is a quote from the DSB FAQ on Reefkeepers:

"How important are the sandbed animals?
They are the single most important component of the sandbed. These animals perform ALL stirring, detritus cycling and general maintenance functions. This is really the key bit to get across. Without healthy populations of these animals, the sandbed will not function properly. Here, let me pull out some more from Ron's talk...
"The sediment infauna process organic material turning it into organism tissue, gas, or dissolved organic material.


A healthy and diverse sediment infauna
- prevents the accumulation of organic material in the sediment.
- feeds the filter-feeding organisms in the system.
- promotes and maintains the biological filter"

It also prevents the formation of dead zones which would lead to the formation of hydrogen sulphide pockets."

Now perhaps you understand my point that the fauna in a DSB is required, which was the main subject of my original post. Your final comment about Dr. Jaubert's recommendations about gravel depth is a debatable topic by itself. There have been numerous experts, scientists and hobbyists who have experimented with various gravel depths and reported their results. There are a few books out on the subject also on this if you wish to research it. Just because Jaubert has an opinion on a specific number of inches something should be, doesn't mean he's wrong, right or the variable isn't flexible. This is common sense of course, and I beleive there are many depths of DSB's out there, depending on how much tank real estate one is willing to give up to it. As stated before, I've ran all of my plenums with a total height of between 5 1/2 to 6 inches and they work just fine with nitrate at 0ppm.


To argue my original point(again), I feel a DSB is an inherantly flawed approach to maintaining a reef tank. You, and numerous others do and can disagree with me. I'm OK with that. My philosophy on maintaining a reef tank is to maintain the most stable controlled enviornment possible for the tank inhabitants. A coral reef is a very nutrient poor area of the sea. They are used to extremely good water chemistry and the water is very clear and has a high ORP with a low DOC. A plenum system, not requiring the huge biomass teaming within the DSB, has a much lower BOD, and if detritus is kept in check, the ORP is high with the DOC kept low. Myself, along with other plenum advocators beleive nutrients in a closed system should be kept as low as possible for long term success.

One of the catchwords floated around prevolantly with DSB is "biodiversity". By including all of the micro-organisms within the bed, some feel that their overall system is more stable and closer to nature. Beleive it or not, in the actual ocean there are blue whales, tuna fish, barracuda, sea lions and millions of other things that would make your tank more "biodiversified", could you cram them in your tank. The point here is not only is this high bioload unnecessary by using a plenum, it can be detrimental to the overall success of your DSB system. Imagine if you will identical tanks setup, one with a properly constructed plenum and one with a properly setup DSB. Both tanks are operating perfectly. Now something catostrophic happens, like a critical pump, such as the circulation pump fails, or there is a sustained power outage. While neither tank benefits from this, the DSB tanks will die much quicker. Why, because it's biological oxygen demand is so much higher, the sand bed will literally choke the tank from O2 very quickly, killing off much of the life. You don't think things like this will ever happen, you might have a UPS or a generator. Not everyone does, and some parts of my town lost power for over 5 days this past summer during a storm, far beyond the capabilities of a UPS. I've also heard of people having mysterious fish deaths with DSB's more frequently than with plenums. It's probably for the same reason. A DSB has a very large localized BOD. Since water flow over the bed must be restricted to keep from disturbing it, circulation isn't what it could/should be. If you add to this situation a benthic fish or other animal, lying close to the bottom at night, when O2 levels are lowest and CO2 is highest, you can see why some of these mysterious deaths could have happenned.

The respiration as a result of the DSB's inhabitants' metabolism also forms large amounts of CO2, which naturally creates a drop in pH and alkalinity. While the carbonic acid formed can dissolve some of the carbonate within the substrate to buffer this effect, the oolitic sand is not built for the purpose of controlling water chemistry such as the larger grain substrate of a plenum system, and it's chemical buffering capabilities are more limited. If the DSB is unable to keep up with nutrients, it's very easy for it to start accumulating phosphate as it can go in and out of solution easily. It generally precipitates on calcium carbonate at the surface, and microbial mineralization only hurts in your efforts to control problem algae.

Since detritus tends to accumulate in a DSB system, heavy protein skimming is almost mandatory. Without this, DOC would build up without frequent water changes. I run, and have seen and heard of many other plenum systems running completely stable for years with no protein skimmer. Because the tanks are kept more "sterile", as I believe a closed system should, the need for heavy or any protein skimming is often not warranted. The lack of necessity for a protein skimmer also means less stripping of trace elements from the water. Many compounds added to a tank within a bottle of trace elements are almost instantly skimmed off before the corals even "get a taste" of them. The only other filtration I use on my tanks is a very small amount of passive chemical filtration with a good resin such as Purigen. The only reason this is done is to keep any yellowing that could be in the water in check to keep it as crystal clear as possible.

A plenum is not for everyone, it IS more work than a DSB system, and not everyone actually wants to do that work. A DSB system also does have more readily available food for filter feeding corals and invertebrates. I like to control what goes into my water and feed my corals accordingly. That in no way means that I'm starving my corals, as some would be quick to accuse, but I'm also not supporting a large biomass in-tank just to feed them with. There is a fine line between growth and long term stability. Giving the corals all the food they would like will make them grow faster, yet your DOC also increases. Giant clams for instance grow much faster if a direct source of nitrate is readily available, as they can consume it as an energy source. That doesn't mean that nitrates should not be kept at zero or near zero levels within an aquarium. The key to success is trying to maintain your bioload while keeping the tank as nutrient poor as possible. Just because a tank seems stable at the moment, with no detectable nitrate doesn't mean it isn't being stored within the live rock or sand bed. If your nutrient input is greater than your output, the system will eventually crash.


Whenever you find that you are on the side of the majority, it is time to reform. -Mark Twain

 

[Minh Nguyen]

cwills,
What is THE DIFFERENCE between a sand bed and a plenum sand bed? The difference is the empty space at the bottom of the plenum bed. This space was put there because believe that anoxic sand bed is deadly to the tank inhabitant. This, in my experience and according to the vast number of aquarist that use DSB, is NOT TRUE. Let me put it again: The reason why plenum was invented in the first place was not true therefore plenum is not needed. I am sure that you cannot come up with a single instance where someone have their tank wipe out due to gases release from a deep sand bed. This idea is just an idea in someone’s head. I got several pistol shrimps in my tank that would dig deep burrow into the sand bed. Let me tell you that they and my tank are fine.

The basic reason that plenum and DSB works in lower nitrates is the same. One can use the same substrate that you use in your plenum for a sand bed and it will work just as well. I have used crush corals for my sand bed in my 100 g tank in the past. It works quite well. Nitrates always measure at undetectable in that tank. I like to use fine deep sand bed at this time because I have various worms that I put into my sand bed that goes very deep. I like to provide adequate living quarter for them.
In an essentially close system like a typical reef aquarium, one needs to balance the input of nutrient with the output from the system. This fact hold true for BOTH sand bed and plenum systems. If the input continues to be higher then output, the system will accumulate nutrient and crash. This is a well know fact (at least to me). How one obtain this output is depends on the aquarist, not whether the tank have plenum or DSB

There are many ways to maintain a reef tank. My reef tank is doing very well and my corals grow like crazy. I am sure your method works too, however, I am a lazy person. I look for the easiest way to get things done. I will wait the time that my tank will crash as per your prediction. Please don’t hold your breath because I am certain that if you do, you will long dead if and when the moment come.

Your long arguments regarding the fauna in the sand bed is irrelevant. The sand bed does not need to be load with organism in order for it to work I just like it better that way.

[ February 07, 2002: Message edited by: Minh Nguyen ]</p>

 

[[email protected]]

Nimh

I'm sure we could probably be running a successful reef on an UG filter if we really wanted. If you're happy, I'm happy. This plenum/DSB arguement has been made way too many times anyway. Just trying to throw mikey98 a few relevant points I feel are important to the debate. Ultimately it's up to him to make the most intelligent and informed decision on what sort of philosophy he wishes to implement towards his reef.

I wish him and you continued success in your endeavors.

 

[BiGBOi]

I run plenum with 4" of Caribsea's Special Grade Seaflor Aragonite amd 2 riopowerheads with spraybar and that's all. No skimmer. Haven't done a water change in 10 months. Calcium 480,Alk 9 dkh,nitrates 0, nitrites 0, ammonia 0, ph 8.3. Tank contains Soft corals, LPS, SPS, and clams. All all are well and growing. Thats all I have to say. You make the decision.

 

[mikey98]

Ok one last question, which one has been around the longest?

 

[mikey98]

Ok one more. How deep does a plenum system need to be? And how deep does a DSB need to be? I want to have some area for my corals and fish to move.

 

[mikey98]

DITO

 

[KanUCme]

DSB 2"-6" inches according to my book. I am running about 2" of sand. No plenum.