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4K views 4 replies 4 participants last post by  geedoug 
#1 ·
Hi there,

I am setting up a new 125 gallon reef, and I am wondering, should I go with a plenum or not? I would probably have a 3" sandbed max,
with the screen in the middle and about 1" of void space. However, I have red some
articles by Thiel and he claims that a plenum is a nutrient time bomb waiting to go off. Has anyone had bad experience with this type of system? Would I be better off with just sand and now plenum?

Roger

rtatum5791@aol.com
 
#2 ·
Hi Hodgie.
The plenum,
Grain sizes recomended 1.75mm to 4mm smaller grain sizes can block up meshes and bind.
Besides being
an area to contain a slight bit more oxygen than the above sandbed, is also
a normal and needed reservoir for certain constituents such as nitrate.
Nitrate and other constituents are temporarily store there and used by the
bacteria above in their metabolism processes and/or as foodstuffs. Draining
the plenum only upsets the processes and harms the balance/equilibrium in
the area. People who had drained their plenum and found nitrate above that
in the bulk water panicked and wrote unflattering articles about the plenum
system thinking they had discovered a fault. Little did they realize what
they saw was a normal and helpful attribute of the system.
My understanding on the plenum using aragonite sand
The semi-stagnate cavity mimics the reaction that take place in deeper sediment beds of the ocean.
different bacteria populate different parts of the structure according to the amount of oxygen that gets there.
These bacteria reduce the amount of three waste products that are found in the water of the entire tank.:
ammonia nitrites nitrates.
these bacteria also slightly acidify the water in the bed to slowly dissolve the sand.
This is called dissolution.
If the PH in the aquarium itself is low it can dissolve more of the sand,which releases buffers.
These buffers work to bring the water back into the normal range. (sounds good?)
As the sand dissolves it also helps regulate several element levels like calcium,carbonate and strontium .
Microbially, crushed coral would provide the same benefits as would
aragonite. The only difference is that aragonite does help supplement the
carbonate buffering system somewhat. Where it is too expensive, crushed
coral will suffice and alkalinity can easily be controlled via a calcium
reactor
As far as I see a plenum it creates a nitrate reduction system that's it and in certain circumstances it may be more helpful than a deep sand bed for nitrate reduction I.E. a shallow reef crest set up with very high water flow may keep kicking up very fine sand not good for SPS corals.
An infauna live deep sand bed will also reduce nitrates as well as a plenum but a deep sand bed due to fine grain size will support a diversity infauna that will give the added benefit over the plenum.
They will keep the bed turned over and remove detritus and will give a diversity of natural live plankton larvae to the system that a plenum will not, which is a major advantage.
Also a plenum needs the top inch regularly disturbed more maintenance involved this is.

Bob Goemans recommends the grain sizes for a plenum be between 1.6mm to 4mm

Rob Toonen info on.
Southdown Tropical Play Sand
Size breakdown of the sand:
>500 um (= 0.5 - 2.69 mm): 14% (largest particle 2.69 mm)
>300 um (= 0.3 - 0.5 mm): 32%
>250 um (= 0.25 - 0.3 mm): 16%
>180 um (= 0.18 - 0.25 mm): 20%
>125 um (= 0.125 - 0.18 mm): 13%
>100 um (= 0.1 - 0.125 mm): 3%
>50 um (= 0.05 - 0.1 mm): <1%
<50 um (= 0.001 - 0.05mm): <1%
Ideal for a DSB=(Deep Sand Bed) but not for a plenum.

A little light reading below.

Sandbed References

HTH
Martyn

[This message has been edited by Martyn (edited 10-16-2000).]
 
#3 ·
I've just completed setting up my new 250G w/plenum, etc. for many of the reasons Martyn has given above. Also, the current 125G FO I have has been running 5 years now w/plenum...and has been very successful. (and very low maint. tank, might I add plenum and skimmer are THE filtration for the system....that's it. 15% Water change every 2-3 mos. Argamight in the top-off).

Water parms have always stayed proper, includes Nitrates never over 10ppm, (pretty good for a tank fed twice a day).

The key to the plenum is the grain size of the sand and ensuring that the plenum area is never 'disturbed'. This can occur if it is either not setup properly, or if you keep inhabitants that bury/dig into the bed (ie. Jawfish, burrowing wrasses, even Anemones that bury their 'foot' into the sand can go to deep to disturb the plenum area).

With this in mind, IMO the plenum provide more benefits (some mentioned by Martyn) and better denitrification than a DSB w/no plenum. A good set of hermits will keep the top layer stirred (no manual stirring needed). Seed the bed with some LS/Grunge add some LR for some biodivirsity.

The bad rap seen on some boards are normally from systems where the plenum has been disturbed or not setup properly (often by folks trying to 'improve' upon the tried and documented ways of setting up a plenum). As with any new setups, if you take your time and do things slowly....you'll have success.
 
#4 ·
Originally posted by Jaffo_botz:


With this in mind, IMO the plenum provide more benefits (some mentioned by Martyn) and better denitrification than a DSB w/no plenum.

I disagree. A properly setup deep sandbed (4-6 inches) will provide *all* the benefits of a plenum, but without the difficulties involved in creating said plenum. Sand stirring should be provided by sand dwelling creatures such as bristleworms, spaghetti worms, and sand eating cucumbers such as tiger tails.

If you do a search in the #reefs library, for Shimek, Borneman, Paletta and Lowrie, you should come up with enough information on both types of sandbeds, to make an educated decision on which method will work best for your needs.

HTH

------------------
Jim Fox
http://www.geekopolis.com/reef/nos4a2/

In the sea of life, you're just a minnow...you live your life, insecure...
 
G
#5 ·
Great question and very good replies and references. This goes to show there are many ways to reach the same goal.
Do Plenums work? Yes
Do Deep Sand Beds work? yes
Can either fail with disastrous results? Yes
Bottom line what ever method you choose, study up and go slow. PAtience isn't a virtou its an absolute must.
Personally I am happy with the results I have had with DSB, so I will stick to it

------------------
I thought I was me, but we were wrong
email: geeflipr@internetcds.com
 
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