Deep Sand Bed

Adam,

I'm not very experienced, but I just put in the sand, directly into the tank.  IMO, if you want a more stable foudation, you could pour half sand, eggcrate and the rest of the sand.  On RC it states that will keep any burrowing fish and critters out of the anaeroic section of the DSB, keeping the DSB intact.

Just my inexperienced opinion though!

Sean

Another method of keeping animals out of the bottom of the DSB is to use some fiber glass window screen (Sean at Aquatica in Orem does it this way).   In my tank, I put down ~1.5" of sand, screen, then another 2.5" of sand.  I don't have any burrowing animals, but my nitrates are undetectable so far.

-Tom

The "shallow" DSB's I've set up over the last year for myself and others, seem to be doing just fine. I believe in the power of 1 to 2 inches of Oolitic sand with a blanket of larger particle aragonite.

As you know, I was one of the first to jump onto the Plenum "bandwagon" back in the mid-90's right after Jaubert's system was introduced to the hobby via the Sea Scope. After about four years of plemums, my tanks gradually "lost" their plenums and for 5 years now I honestly see no difference.

And the scare about the killer rotten egg gas is just that, a scare, of which I alone am the only person I have ever heard of that has had an experience with it. (a separate freshwater incident)

Without the need to conserve the integrity of a plenum, the entire sand bed can be home for whatever burrowing or digging animals you want and they will love you for it!

My tank has 3"s of fine sand and 2''s of more coarse. I have barely been able to ever detect any nitrates/nitrites in my tank. The plenum method almost seems like a hassle to maintain.  I have a hard enough time keeping up with water changes to the tank let alone water changes underneath the plenum. But then again I never have used plenum.
My .02 worth

taper, you don't change the water under the plenum... it's just there.  The underlying principle of a plenum is diffusion of nitrates/nutrients into, through and back out of the bed.  Diffusion is a strange form of mass transfer... it's motive force is just a concentration difference (of any particular compound) between the bottom of the bed/plenum and the tank.  Since the water concentration is the same in both places there is no real water movement through the bed, but nutrients can be diffused through it from an area of higher concentration to lower.

Mark, a properly applied plenum would not make a good sand bed at all.  Jaubert recomended sand grains much too big (2 - 5 mm).  According to Shimek most of the sandbed infauna would not survive in this material.  Jaubert's bed is for bacteria not worms.   And the screen is only necessary if you have digging fish (gobies, ect) in the tank.

The article referenced above is a good read.  For a better explaination of deep sand beds, read Shimek's latest article:  http://reefkeeping.com/issues/2003-06/rs/feature/index.htm

Maybe Mark's suggestion of 3" oolite under 2" caribseafloor is a nice workable compromise (doesn't Shimek suggest deeper beds than that?).

I'm not encouraging the use of plenums (or dsb for that matter).  I just wanted to clarify a few things.  Really, the fact that so many aquarists are successful using either method must mean that either one would be a good choice.

Piston, I don't think you need a sand star in your bed for water movment... it's the small worms that move the water through the bed (mark correct me if I'm wrong here).

My vote is of course, no screen.

Adams words about sand sifting stars sound wise to me.  Question: How much life will they eat and how large of an aquarium, or rather how much sand area is required to adequately handle a ssstar and still have life in the bed for other fauna?

Comments on Jon's post: I actually placed an airline tube in the plenum of my sump before adding sand. After 6 months I unplugged the tube and siphoned out a cup of water. Ohhh did that water smell rich! I should have checked Nitrogen levels for some empirical proof, but our typical test kits probably would not not been accurate at the high levels. This plenum water was a rich organic soup. It smelled rich enough to use for gravy (bad example). My experience shows that the compounds do not pass back and forth. To describe the plenum as a nutrient sink would be accurate. That's the real reason why plenum users must take extra care to protect the area from diggers! Again, I had an experience with this. The plenum in my 75 (this was a different plenum, separate from the one with the airline tube just described) had no screen to protect it and a damsel decided to dig a hole sometime before a year had elapsed. Macroalgae bloomed.

My recommendation for substrate depth is NOT 3" and 2" as Jon stated. My original idea was to use Utah Oolitic sand to make an aesthetically pleasing "shallow" DSB. I cannot say that a deep bed of Oolitic is wrong, especially since Shimek says it is right! What I continue to recommend is an aesthecally pleasing 1-2 inch layer of Oolitic and a 1/2 inch layer of larger particle aragonite substrate. I know it sounds inadequate but it works! And it gives more tank space for the things we like to have showing instead of sand!

And Yes Jon, I believe it is the tiny critters in the sand that help circulate water, ie., nutrients. This is in agreement with Ron Shimek.

Adam, my bad, I misunderstood the question.  When I hear screen, I'm thinking plenum.  I'd say the benefits of a screen do not outweigh the potential drawbacks.  My vote is no screen.

And yes Mark, it's not uncommon (from some of the stuff I've read) for the plenum water to be very nutrient rich in some applications, hence the suggestion for a screen.  Sprung isn't the only one to say it but that quote from his article (above) is straightforward... 4 inches of gravel above a plenum works better then 4 inches of gravel without a plenum.  Either their observational skills are lacking or there is "something" good happening with a plenum.

Jon has pointed us to a very important article by Julian Sprung. Julian visited us last July and this came out in September. Perhaps he even alerted us to something coming out. I can't remember but anyway, since I don't read so much of the hobby literature anymore, I really appreciate Jon bringing this to our attention.

Everyone may want to read this article. I have recopied the link here:

www.advancedaquarist.com/issues/sept2002/feature.htm

Bob Goemans must have jumped for joy when this came out! He was a guest a few years ago when we met at the U of U. He was so sure that a plenum was the best and yet had no comparative proof nor any scientific data or explanation to support his claim. Sprung's article does not give us any empirical evidence either, but he is no dummy and so I believe he has some data and/or comparative observation to back up his statements. He even admits at one point that his observations did not compare the plenum with the Shimek DSB.

This is so interesting to me! I love it!

One last thing.  Eric Borneman had a similar issue with Sprung not backing up his stance with data.  Although not related here is the article.

http://www.reefkeeping.com/issues/2002-05/eb/feature/index.htm

For those that don't want to read the entire Toonen article here is a snippet of his conclusion.

"In my opinion, the addition of a plenum is an additional level of complexity that is neither necessary nor beneficial over the inclusion of the deep sediments themselves."

"To come back to the original question posed by the article that prompted this reply, "are plenums obsolete?" I would have to say that the word obsolete does not accurately reflect my feelings on this matter. I would rephrase that question to "are plenums necessary?" and answer with a confident "no." "

"In conclusion, I am not trying to convince anyone that the addition of a plenum is likely to hurt the functioning of a healthy sandbed, but in my experience the addition of a plenum didn't seem to really help either."