Discussion in 'Sand' started by reefnJeff, Feb 16, 2012.
Have any of you used this system in your tanks with success and how did you construct it?
Had a 55G once with undergravel filter. Ran water through the filter for a few weeks then capped off the riser tubes, leaving the plenum under the sand for an anaerobic zone. System ran for a couple of years before we took the system down. No problems and low to zero nitrates.
I've read a lot on them and they used to be the standard from what I read. Just have fallen out of favour recently for newer methods. I have never used one myself, but I do think that they are a bit dated and have been replaced for a reason. Just my 2 cents.
I heard this sytem was really good on nitrates, what was suggested to me was to put crushed coral on top the undergravel filter, then place a screen on top of the crushed coral, then live sand on top the screen, just not sure how this system works.
What are some of the newer methods? I'm kind of old fashioned in my thoughts and age but I always believed newer is not always better.
Algae turf scrubbers
Deep sand beds
Carbon dosing i.e. vodka, vinegar or biopellets
You name it. There are many methods with varying degrees of effectiveness.
I think part of the problem with the plenum system was that it didn't provide for a place anaerobic bacteria as there was constant movement through the substrate. This is a very important part of the nitrogen cycle in our tanks. Also they would collect detritus and become nitrate factories overtime without proper maintenance (we tend to get lazy overtime and why add more work). I've never used this system so I could be wrong.
Now a days, I think most would recommend a sump/fuge (remote area for filtration). Although all that is really needed is an area for bacteria to colonize (Live rock) and circulation. A protein skimmer can certainly help with export of wastes.
You won't find many tanks on here that are using a variation of this method.
Really to answer the question of current methods would take a text book worth, so I've tried to give an example, there really is lots out there.
The way I had my under gravel filter did not have constant movement through the substrate. It was seeded initially by pumping water through it then capped and sealed. The area beneath the filter became an anaerobic zone. Worked great.
I agree! Just I don't think this is how it is designed to work.
Interesting really! So what would be the difference between the newer deep sand bed system and this system with deep layers of sand bed over the Plenum?
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):
For what it's worth. There are other plenum articles on that board too.
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