Updated Aug 4, 97
I have read the various posts on plenums with interest and can find both advocates of plenums and non-advocates. The other document on Plenums in the Latest Site Changes describes my experience with a plenum on a large aquarium at my house, and the testing I did over a one year period of time. I have updated that article with more detail, especially with regard to the materials used to make up the layers.The article generated quite a bit of reaction from certain hobbyists who feel that I could not write off "plenums" based on that one experience alone.
That one experience was a fully documented one and the only one on which I have all the data needed to put together a complete overview on a timeline basis of what the water in the plenum actually went through, and how the nutrient levels in it behaved.
It is clear from that experiment that they rose to levels far above what I think anyone would have expected.
Comparing Jaubert's systems to our aquariums is risky as he uses different techniques, very large aquariums and no skimming and semi-open systems with water changes. Aquariums operate differently, and calling a set up with a plenum and a skimmer and a closed system "Jaubert" method operated is on the borderline as the two types of systems are not identical.
Modified Jaubert is perhaps a better terminology as that is what we all do when we take his precepts and then start adding a skimmer to it and operate a closed system.
A reader pointed out that this is the reason he does not refer to his system as a Jaubert one but, rather, a live sand with plenum. I fully agree with Raymond Smith's comments in this respect ( Raymond Smith's Email )
Accuracy of terminology is important and if not used can lead to confusion on the part of people reading this and other related documents (and others in general).
In the system I tested after experiencing problems with other aquariums where water quality appeared depressed based on testing, the sand layer consisted of the typical plenum type set up with egg crate grid 2.5 inches of true plenum space over the entire area of the tank. On top of that were the screens and layers and the layers were thick as described.
A question was asked as to what other problems I had observed in these different systems and whether they were related to just a PO4 build up on whether there was more to it.
There was indeed far more to it than just a steady low non explainable PO4 level which should not have existed as metal oxides were used to remove phosphate at all times. However one problem in such tanks was that very low levels were constant and could not be brought below 0.06 ppm for any length of time. Removing the compound made the PO4 rise to levels of 1.2 to 1.8 ppm in a real short span of time, even though all measures had been taken to prevent PO4 from entering the tank trough any source know to bring about a rise in phosphate (and silicate - which rose as well).
In addition: the corals always appeared to be influenced by a lower water quality level and did not really look "thriving" and certainly not looking "vibrant", as they normally appear when water quality is real high.
It seemed obvious that the water quality was depressed for some reason.
Oxygen levels were lower, the ORP (oxidation reduction potential) tended to want to fall to levels of 220 to 260 mV in approximate numbers, whereas the tanks should have been running at around 400 mV, as filtration and so on was set up to maximize water quality. The reason for this lower oxygen and ORP level could not be explained in any way, other than that something was affecting the water quality that was not being controlled.
The only variable that was not being controlled being the water in the plenum itself, my suspicion was that the source of this overall depressed water quality (in the aquarium) had to do with some exchange of conditions between the plenum water and the one in the tank.
To confirm this, after having experienced this several times in different tanks, I decided to run the timeline test on the large aquarium (see the other document on the Plenum testing at http://www.athiel.com)
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