Deep Sand Beds???

[Brian Prestwood]

Hey All

In case it wasn't clear, our speaker's comments on sand beds contradicted what many of us, including me, have understood for years. If our speaker is correct, our deep sand beds (remote or in-tank) are doing the opposite of what we intend.

To keep this thread productive, I'm not going to mention our speaker by name. I would appreciate it if no one else does either.

Our goal is convert waste to something that is self exporting. Under the right conditions, dictated by oxygen levels, certain bacteria will convert waste to nitrogen gas which bubbles out of the tank. Of course, this does nothing for phosphorous but I'm not going to get into that now.

Our speaker said when a sand bed is sitting on the tank bottom, or sump bottom, with no plenum there are three layers in it, an aerobic (oxygenated) layer, an anaerobic (low oxygen) layer and an anoxic (no oxygen) layer. This is consistent with I've heard. Our speaker said the thickness of these layers is primarily dependant on the grain size of the media. The courser the grain size the thicker the layers. This too is consistent with what I've always heard.

Our speaker gave an example with 2mm grain size. This is much courser than the sugar fine sand we normally use for deep sand beds. In the 2mm grain example, the first 0.5" is aerobic, the next 0.5" is anaerobic and anything below 1" is anoxic.

This is inconsistent with what I've heard from several sources I considered reputable. They said that with even sugar fine sand the anoxic layer doesn't start until 3"- 4" inches down.

Finally, and this is the biggest contradiction to what I understood, our speaker said it is the anaerobic layer between the aerobic and anoxic layers, that converts waste to nitrogen gas. The bottom anoxic layer converts waste to ammonium (fertilizer). In other words, bacteria below the anoxic layer is converting waste to fertilizer, not nitrogen gas as we intend.

Our speaker said a plenum maximizes the thickness of the anaerobic layer and thus the efficiency of the sand filter by introducing oxygen from below as well as above the sand bed. Our speaker was unsure of the source of the oxygen from below but noted that the oxygen levels tested consitently.

Our speaker recommended a 4" layer of 2mm sand on top of a plenum with a 1/2" layer of water under it is a good design. Our speaker remotes the sand bed so the fauna can't affect it.

If it were't for the fact that several reputable sources recommend deep sand beds, I'd believe I simply mixed up anaerobic and anoxic layer dwelling bacteria.

Comments?

Has anyone found any quantitive analysis on anaerobic, vs anoxic, layer dwelling bacteria producing nitrogen gas?

Has anyone found any quantitive analysis that contradicts our speakers comments plenum oxygen levels?

[CaptiveReefSystems]

so how was the speaker. Am I sorry I missed it?

[Justin74]

Finally, and this is the biggest contradiction to what I understood, our speaker said it is the anaerobic layer between the aerobic and anoxic layers, that converts waste to nitrogen gas. The bottom anoxic layer converts waste to ammonium (fertilizer). In other words, bacteria below the anoxic layer is converting waste to fertilizer, not nitrogen gas as we intend.

This is how I understood it to be as well.

What I am missing is why he suggests that it be removed from the fauna. This is what I thought makes deep sand beds work. I was under the impression that alone they can't work without the worms and such burrowing elaborate networks to bring oxygen to the anaerobic bacteria for the nitrogen process. I would assume you would use a raised plenum if you didnt have access to fauna and was attemtpting to mechanically emulate this.

-Justin

[shiveley]

so how was the speaker. Am I sorry I missed it?

well, if I remember correctly, he and/or his associates invented the plenum, undergravel filters, protein skimmers, and the turbo snail, while also disproving the effectiveness of every other method of biological filtration available.

atleast, that's how I interpreted the presentation; but I could be wrong...

[MrMikeB]

Brian/MARS BoD -

Would it be possible to get copies of the presentations made available on the website of our speakers? There is a ton of good info in these presentations that I wish I had a copy to review when I am not so inebriated . ;)

Steves presentation on electricity should be enough for me to rewire my entire house, and Phil had some really cool footage on the Florida reef that would be very timely given my upcoming trip.

And this last one - well I need to review that one more time before addressing the issue with the DSB to be sure I got the message right (was not taking many notes).

[jtarmitage]

The meat of his presentation can be found in couple of articles on his website, here is the link: http://www.saltcorner.com/1024/index1024.htm
I think that the real problem here is that he and others have tried to figure out how the plenum functions, but we don't yet have an understanding of the biology and/or physics involved, to which he admitted. I am curious to know how many MARS members have had, or currently have plenums. I have used them on soon to be 4 tanks for the past 11 years, and have had nothing but success, albeit without a true understanding of the process' taking place.

Shiveley, Jaubert created the plenum, the speaker was the first US UG user, the reference to protein skimmers was that he started using them before they became popular in the US, while it does sound like he and his associates are taking credit for 'Turbo snails', and lastly, which I was rather impressed with, was that he didn't trash other methods as many of us are guilty of, he merely suggested that the plenum was a better long term method(with the glaring exception of his blast on the Mud method, all the while saying he had no proof, and had never even seen the system in person, which was in poor taste). The failure of the plenum system is lack of maintainance, which I would agree is the reason for failure for most any of the substrate methods.

[juaninsac]

<a href=showthread.php?s=&postid=10390932#post10390932 target=_blank>Originally posted</a> by Brian Prestwood
Hey All

In case it wasn't clear, our speaker's comments on sand beds contradicted what many of us, including me, have understood for years. If our speaker is correct, our deep sand beds (remote or in-tank) are doing the opposite of what we intend.

To keep this thread productive, I'm not going to mention our speaker by name. I would appreciate it if no one else does either.

Our goal is convert waste to something that is self exporting. Under the right conditions, dictated by oxygen levels, certain bacteria will convert waste to nitrogen gas which bubbles out of the tank. Of course, this does nothing for phosphorous but I'm not going to get into that now.

More precisely it converts nitrate to nitrogen gas.

Our speaker said when a sand bed is sitting on the tank bottom, or sump bottom, with no plenum there are three layers in it, an aerobic (oxygenated) layer, an anaerobic (low oxygen) layer and an anoxic (no oxygen) layer.

Some huge assumptions being made here, and I hope it's an error in translation. There is not necessarily an anoxic layer or even anoxic areas in a sandbed, even a deep sandbed of 4-6". Depends on the grain size, depth, infauna, current over the bed, etc.

This is consistent with I've heard. Our speaker said the thickness of these layers is primarily dependant on the grain size of the media. The courser the grain size the thicker the layers. This too is consistent with what I've always heard.

Our speaker gave an example with 2mm grain size. This is much courser than the sugar fine sand we normally use for deep sand beds. In the 2mm grain example, the first 0.5" is aerobic, the next 0.5" is anaerobic and anything below 1" is anoxic.

This is inconsistent with what I've heard from several sources I considered reputable. They said that with even sugar fine sand the anoxic layer doesn't start until 3"- 4" inches down.

Finally, and this is the biggest contradiction to what I understood, our speaker said it is the anaerobic layer between the aerobic and anoxic layers, that converts waste to nitrogen gas. The bottom anoxic layer converts waste to ammonium (fertilizer). In other words, bacteria below the anoxic layer is converting waste to fertilizer, not nitrogen gas as we intend.

This is correct. Nitrate is converted to nitrogen gas in a low oxygen (anaerobic) environment. Again, though, properly constructed DSBs do not necessarily have anoxic layers.

Our speaker said a plenum maximizes the thickness of the anaerobic layer and thus the efficiency of the sand filter by introducing oxygen from below as well as above the sand bed. Our speaker was unsure of the source of the oxygen from below but noted that the oxygen levels tested consitently.

Our speaker recommended a 4" layer of 2mm sand on top of a plenum with a 1/2" layer of water under it is a good design. Our speaker remotes the sand bed so the fauna can't affect it.

If it were't for the fact that several reputable sources recommend deep sand beds, I'd believe I simply mixed up anaerobic and anoxic layer dwelling bacteria.

Comments?

Has anyone found any quantitive analysis on anaerobic, vs anoxic, layer dwelling bacteria producing nitrogen gas?

Has anyone found any quantitive analysis that contradicts our speakers comments plenum oxygen levels?

I don't think you'll find much quantitative analysis about bacteria in sandbeds producing nitrogen gas because it's, practically speaking, hard to measure such a thing. :) Dr. Rob Toonen and Chris Wee did a controlled study of deep vs. shallow and coarse vs. fine sand grains and their affect on nitrate levels in an aquarium. This was presented at IMAC 2004 and I assume it's available online if you search. In TRA vol. 3 Delbeek and Sprung comment on this study with some thoughts of their own, as well as go into a lengthy discussion of plenums and DSBs. Good reads all.

My thoughts: There are several ways to skin a cat. I have seen tanks using lots of different methods and many seem to work long term. I found it laughable when people were yanking their sandbeds because someone told them it would make their tank crash after 5 years. I've seen glorious looking decade old tanks with big fat deep sandbeds. Threads titled "My tank crashed....and I have a DSB!" likewise scared a lot of people. Lots of post hoc ergo procter hoc logic going on there. Long story, short--if what you've got is working for you, I say stick with it.

[funman1]

Hey Mike here is a link to my presentation.
It includes the videos and everything, so it's really big (30)megs
Just unzip in it's own folder and it should work just fine.

http://www.steveries.com/temp/MARSElePre.zip

~Steve~

[CaptiveReefSystems]

well, its good to see a speaker generate this level of conversation. Keeps you thinking and the brain sharp.

[Brian Prestwood]

Bruce

The talk was good. He moved through the history part at a good pace. The contemporary part had a couple of very good tips.

[Brian Prestwood]

To quote jauninsac...

This is correct. Nitrate is converted to nitrogen gas in a low oxygen (anaerobic) environment. Again, though, properly constructed DSBs do not necessarily have anoxic layers.

I think it is fair to say someone has a fundamental mis-understanding. If it is me I'm in good company. I just read another article (Reef Hobbyist Summer 2007 issue) that claims DSBs do have an anoxic layer and that denitrfication occurs in the anoxic layer.

[juaninsac]

<a href=showthread.php?s=&postid=10402462#post10402462 target=_blank>Originally posted</a> by Brian Prestwood
To quote jauninsac...



I think it is fair to say someone has a fundamental mis-understanding. If it is me I'm in good company. I just read another article (Reef Hobbyist Summer 2007 issue) that claims DSBs do have an anoxic layer and that denitrfication occurs in the anoxic layer.

From Delbeek and Sprung vol 1 p 34:

"The nitrate that is produced by nitrification or released by nitrogen-fixing cyanobacteria has a variety of fates. It can be used in the biochemical pathway of respiration by either obligate or facultative anaerobic bacteria. These bacteria reduce nitrate to nitrite, and eventually to ammonium, producing nitrogen and nitrous oxide gases as waste. These gases are then released into the water and are usually either lost to the atmosphere or absorbed by cyanobacteria. This process is generally called denitirification. Since denitrification occurs mainly in the absence of oxygen, it is limited to sediments and anaerobic microhabitats such as coral heads. It has been shown that nitrification and denitrification can also occur in aerobic layers. Here anoxic microsites within fecal pellets and detritus provide a habitat for anaerobic bacteria, while being surrounded by aerobic pore waters."

I am admittedly confused about the exact distinction between "anoxic" and "anaerobic", and I don't know that there is a universally agreed upon quantitative difference between "little oxygen" and "no oxygen".

When I hear aquarists talk about anoxic regions of their sandbed, I understand them to mean black areas where hydrogen sulfide (bad) is being produced. If the speaker claimed that these areas are not only present in every deep sand bed but constitute an entire layer that covers the footprint of the tank, then I strongly disagree. Plenty of people have torn down their sandbeds to find otherwise, myself included.

Randy discusses tearing down his sandbed here:
http://www.reefkeeping.com/issues/2005-12/rhf/index.php

[juaninsac]

<a href=showthread.php?s=&postid=10402462#post10402462 target=_blank>Originally posted</a> by Brian Prestwood
I just read another article (Reef Hobbyist Summer 2007 issue) that claims DSBs do have an anoxic layer and that denitrfication occurs in the anoxic layer.

It's here in case others would like to read it.

http://reefhobbyistmagazine.com/currentissue/volume1_issue2/pages/rhm_summer_2007_08.htm

:D

Thanks for bringing up this topic Brian!

[Thales]

In the reef hobbyist article I used anoxic to mean simply low oxygen, defining it in the third paragraph before the DSB section. I didn't mean to imply that there were regions in all DSB's that are anoxic in the way your speaker was using the term. Sorry for any confusion. :D

[Brian Prestwood]

juaninsac

Thanks for the quote from Charles. He seems to disagree with our speaker.

Thales

I've heard anoxic defined as no oxygen and very low oxygen as compared to anaerobic which is defined as low oxygen. I think the definition of very low oxygen for anoxic is probaby more accurate but the generization of no oxygen is more useful in explanations.

[Thales]

You betcha - my article is absolutely generalizations. Those words get used differently all the time, even differently in different dictionaries. In your speakers writings, he has pointed out the importance of defining the terms when discussing them.