No Plenum Tanks

This change occured not as a result of anyone in particular, but as a normal evolution based on what many in the hobby experimented with and found to be a better mousetrap so to speak. Mind you, Dr. Eng suggested this method, in other words perhaps, decades ago. LS is therefore nothing new.

This, in itself is kind of normal too as so many things we do in the aquarium nowadays have at some time or another been tried by others, sometimes years ago, but were not pursued to the limit or never made it into general use because the method was not widely publicized or the method came before hobbyists were ready to experiment with it.

Whereas recent writings about this system were based on the Jaubert Method of running aquariums, a method that includes the use of a plenum, the latter now appears to be going out of fashion somewhat. Note that there is no consencus. Some still advocate the use of a plenum but, on the other hand, others recommend against it.

It is a fact that one does not need a plenum to run a real successful reef aquarium with live rock and live sand.

It is also a fact that if what follows happens in your aquarium you may seriously wish to consider its possible consequences on your tank.

Do I say that you should not use a plenum. Not really. All I suggest is that it is not necesarry and that it may potentially become a time bomb in terms of water quality. After reading the results of the testing I did, give it some thought and decide what you want to do.

If you have one now, should you take it down? No but I think you should be aware of the consequences that can potentially happen (as described below) and you may wish to take measure to ensure that they do not.

Check the other document on Plenums (The Plenum Controversy continued) for more details too.

No one has pinpointed the exact reasons but some, including myself, have suggested that, based on testing, the water in the plenum section of the tank gradually increases in nutrient levels (often undesirable ones). These nutrients could leach back into the aquarium for various reasons and give rise to problematic aquarium water chemistries.

I conducted such tests, and the results are an integral part of this document. They may "not" be separated from the rest of the document if the document is posted elsewhere or reproduced in any fashion. Copyright needs to be listed as well and the location of the web site where it was retrieved from : http://www.athiel.com

What I found is that the water in the plenum gradually loads itself up with undesirable compounds. This appears to be progressive, and ever increasing. I was not able to determine whether their was an upper limit to these nutrient concentrations, because I did not conduct the testing with that purpose in mind.

Such a test would however be interesting to conduct in addition to the ones I describe here.

Indeed, the amounts of nutrients found in the plenum are quite staggering when one looks at them over a period of a year or more. The details follow after i describe the tank and related matters necessary for you to get a good idea of what we were dealing with and what may have affected the results.

Below are the results of testing conducted on a 380 gallon tank with an additional 55 gallon sump which ran in Las Cruces NM, at my house for over 5 years. Net amount of gallons due to rock etc. is estimated at 350 gallons. The reason I know this is that we had to empty the tank, and measured how much water went back into the aquarium when we refilled it.

This testing covers a time span of one year and the results are taken from the records kept on this testing. These logs and others are kept in special Lab books from Cole Parmer and at the present time I have over 100 such books, attesting to all the records that were kept. For those familiar with them they are the special ones with waterproof paper and squares on all pages and a hardcover. Of course, over 13 years of being in business (we started in 1984) and a few years before that when I kept records of what was going on in my own tanks, that is not a lot, but is quite substantial anyway.

The plenum was installed in this tank approximately 11 months after the tank was first set up. To do so the whole tank had to be taken apart and all animals and rock removed. The details of the set-up and how all this was done are not important, but I wanted to indicate that the tank was not new, and that it had been running for over 10 months before the plenum was installed. I ran tests for 12 months and then again about 6 months later (the results can be found in the tables below).

Equipment on the tank and other pertinent tank information:

• Aquarium was made by DAS and was of irregular shape and higher than most tanks (31 inches)
• 55 gallon sump filled to about 1/2 height. All additives and all injection by dosing pumps was set to go directly into the sump. Electrodes were placed in the tank not in the sump. Electrodes were in areas with real good water circulation. Electrodes were cleaned every 3 to 4 weeks or as needed.
• Live rock from Tampa Bay Saltwater and from Reef Encrustaceans was added over a period of time and totaled close to 500 pounds before live sand was added to the tank. The usual curing procedures were followed when the tank was set up and each time new live rock was added.
• Live sand from various suppliers, over 400 pounds, was added at the time the plenum was installed. Before that time the bottom of the tank was covered with a mixture of crushed shells and crushed coral making a layer about one inch thick in most areas. The rock was placed on top of this layer
• Large TAT skimmer (modified model 90101 double venturi skimmer) run by a 5MD pump from March. Over the life of the tank other skimmers were tested on the aquarium but the modified 90101 was the skimmer that should really be considered as the one used. With two venturi and a 5 MD pump excellent skimming was the norm
• Four powerheads circulating water in the tank for a total flow of over 1000 gallons per hour (the tank was 8 feet long and it was estimated that although this gave a considerable amount of flow, in hindsight more flow would have been better still. From what I know now and did not know then, I would up that flow to at least 2000 gallons per hour of laminar currents.
• Controllers included pH and redox potential but no external devices were hooked up to them. The brand was the Octopus and I used several Pinpoint ones as well.
• Kalkwasser was dosed by means of a peristaltic pump from Cole Parmer
• Additives used: Liquid Gold and later Vital Gold, KSM, Iodine, Borate and Sodium Carbonate for dKH control. For some time a carbonate hardness reactor with CO2 injection ran on the aquarium but its use was discontinued as the tank stabilized because the unit barely ran more than 30 minutes a day
• Additives were added by means of a dosing pump (Vital Gold, KSM in particular). Another small doser was injecting small amounts of potassium permanganate solution once a day to help reduce the build up of dissolved organic material. This turned out to be unnecessary after a while as the double venturi skimmer was doing an excellent job at keeping such levels low so this was discontinued.
• NoPhosphate and NoSilicate were used to control algae. After the tank stabilized, the need to change these compounds dimished a great deal and although the compounds were used, towards the end they did not need to be changed more than once every 12 weeks or so.
• Hach test kits were used to measure most of water quality levels. Some tests by Merck were used as well
• Ion selective electrodes were tried for some time but this was abondoned because of the difficulty in measuring element concentrations with ISE electrodes in salt water (too much interference from other elements when trying to measure one particular one)
• NoNitrate was used for some time until the nitrates were below 5 ppm total on a constant basis. After that the system maintained itself at low NO3 levels by itself, especially after the introduction of the live sand
• Note that I refer to the No names of these products but they were originally called X- products
• Many sand dwellers from Tampa Bay Saltwater came with the live sand and buried themselves shortly after adding the sand to the tank
• At first the tank was equiped with 4 250 watt 5500 K metal halides (US made). This was later changed to 3 400 watt 10 000 K ones. During the night a low wattage bulb ran for 4 hours
• At one time I experimented with running the lights only 6 days a week, on an irregular pattern but no apparant benefit was derived from doing so and the idea was abandoned
• No water changes were performed but because the evaporation was high, large amounts of KW were added every day in liquid form
• The type of set-up used was the typical plenum, contructed out of eggcrate material, covered with screening, on top of which a mixture of crushed coral and crushed shells was placed about 1.5 inches thick and to which some aragonite was added. Another screen was placed over this layer and on top of that the sand was added.
• The sand grains were 1 to 2 mm. In most areas the sand layer was 3 or more inches thick and in some areas quite a bit more due to the shifting of the sand as a result of current and other water mechanics.
• At no time were there any problems with hydrogen sulfide production or anaerobic activity.
• The aragonite used was a commerical aquarium grade. The crushed coral was too but was made finer by crushing it more (some particle were as large as a 1/4 of a pea but most were quite smaller. The crushed shells were regular sea shells hammered to break them up into small slivers. All this was mixed together and was placed on top of the eggcrate covered with a fine mesh screen so no material could transfer across the screen. Powdered matter had been washed out of the mix before placing it on the screening.

The tank load was moderate to high depending on what one uses as guidelines. Corals included: Catalaphyllia, Scolymia, Clavularia, a green and a red Trachyphyllia, Plerogyra, Pachyseris, Acantophyllia, Actinodiscus, Galaxea, several types of Euphyllia, Lobophyllia and other LPS type corals. One large carpet was in the tank also (Stichodactyla mertensii). Fish were limited to 2 grazing Tangs (Zebrasoma flavescens and xanthurum), Gobies, Hawkfish, Six line Wrasse, several clowns, and others still as well as several shrimp, a flame scallop and a spiny oyster. Quite an assortment inded obtained from various sources and added one or two at a time when the tank had stabilized (and had no sand in it yet).

No photographs are part of this article as many are being used in the "New Marine Fish and Invert Reef Aquarium" book and I do not wish to release the photos before the book. That book is due out in the latter part of October 1997 and is around 900 pages, hardcover, with plenty of photos. It can be ordered at prepublication price on our web site http://www.athiel.com through our secure ordering system.

Tank Parameters (median readings over the life of the tank before and after the live sand was added)

After that period the tank was pretty stable in terms of its parameters and except for fluctuations between day and night and morning and evening nothing much significant needs to be reported as there really was not (some of these are actually listed in the table above where you can see lows and highs for temp and pH for instance).

The reason I measured iron content was to make sure it would not slowly creep up on one hand, and to determine whether iron was uptaken by the corals and algae, which appears to be the case, as Vital Gold and other additives added to the tank were supplying small amounts of Fe each time these were dosed.

It would appear, therefore, that iron is an element that is certainly depleted and needs to be replaced (it is part of the Vital Gold make up so if you use our additive you are automatically adding it to your tank).

I started measuring the parameters of the water in the plenum after the sand was in the aquarium for one month. I then took measurements once a month at 30 days interval. The table below shows the results at timeframe 60, 90, 120, 150 and 180 days. I then skipped a few months in the reporting below (although the actual testing was done) and give you the results for the last months of the testing.

The method used for this was to insert a real small pipette through the sand layer and screening to the bottom of the tank so its end was definitely in the water that constituted the plenum. The glass pipette was left in place so no "holes" would be made (interestingly enough, it did not take long for that pipette, placed in the left corner of the tank, to be totally covered with coralline algae).

Below are the results for NO3, PO4, SiO2, pH and and O2. I did not measure any other parameters.

It would appear that the progression of nutrients is gradual and upwards and that oxygen falls and so does the pH.

When I measured the pH after 18 months of running the tank and before taking the plenum out (that was an exercise!) the pH was actually 3.9 and the oxygen level had fallen to below 3mg/l. At that time NO3 was close to 900 ppm.

Of course to take all these test I had to use dilutions in certain cases as none of the tests measured in such high ranges. I remultiplied my results by the dilution factors to arrive at the end results.

Based on this test and a test on one small tank, for a shorter period of time where I discerned the same trends, the conclusion to be drawn from this in my opinion, that plenums pose a potential problem for the hobbyist and the animals in the tank.

Indeed:

• These nutrients can leach back into the aquarium by means of osmosis
• Any break or rupture or shallow area of the layers could result in these nutrients seeping back through into the water

If this happens to a large extent, the tank is going to be in real bad shape as large amounts of all the nutrients will suddenly mix with the tank's water.

If a slow osmosis of nutrients takes place, the tank will go through unexplained problems and algae outbreasks that cannot really be accounted for. Alternatively or in addition nitrate, phosphate and silicate may show up in the tank that the hobbyist cannot explain in terms of origin. Of course no one would suspect that the build up actually comes from nutrients that leach back into the tank's water from the cesspool of nutrients that the plenum has become.

For this reason I no longer use Plenums in reef tanks and no longer recommend them.