Plenum live sand system?

Biggest difference, is that the plenum has water flowing through the sand bed, whereas the way most of us do it, there is no flow through the sand bed. Thus allowing anaerobic activity to take place.

Also as the water passes down through the sand in the plenum system, it draws detritus and organic matter down into the substrate with it, this then decomposes causing nitrate issues.

 

A plenum only has water moving thru the bed while the tank cycles. Once the cylce is complete the riser tube and pump are removed. There is no crushed coral used in a plenum system.
http://www.garf.org/bulletproofreef/plenum.asp This example shows how to build one for a 40 breeder but the lay out is the same for any size tank. I've used this system once but the tank wasn't up long enough to say what the long term benefit is. Nitrates were low during it's life even though there was no skimmer.

 

One method of having low nitrates is to not overstock your tank and not overfeed. ;D

 

I do apologize, thanks for the correction Reefmonkey. I did a quick read through on this system to refresh, if the OP has access to "The conscientious marine aquarist" I found some neat info there on it.

 

Yes! Thanks reefmonkey! I like the plans and I see your point, once the tank is cycled and the lift tube removed, it then would become a total dead zone in the Plenum and nothing at all to cause water movement.

 

The article I am reading says the Jaubert added the plenum to promote slight flow through the sand to help stop the formation of hydrogen sulphide (flow not from pumping, but just from current in tank seeping through to plenum). So basically it's the same as we use but a little flow through the sand.

 

My thought was to have a layer of crushed coral with live sand on that divided by the screen so they don't mix together, thought it would cut back on cost over putting a 4 inch bed of live sand, guess I will have to rethink that. next week all my ordered equipment will start to arrive, excited about that.

 

Stay away from crushed coral. No matter what you do you will end up with trapped detritus which will turn into a nitrate factory. Use grain size similar to Seachem Special Grade Reeflor.

 

I like that garf site, lots of good information in there, thanks again reefmonkey.

 

I wrote this many years ago on plenums (older than post date when I ported it here):
http://www.3reef.com/forums/reef-aquarium-articles-how-tos/sand-dsb-vs-plenum-54324.html

For what it's worth. There are other plenum articles on that board too.