My Plenerific Adventures (Anecdotal Plenum Info)

As a kid, going to the ocean was a big deal for me. I grew up and still live in the interior of B.C., so it was at least 4 hours and a bit to drive to vancouver to see relatives. i was always anxious to get down to a beach and play in a tide pool or turn rocks over to try and find the biggest crab.

The first reef book i read was "The simple guide to marine aquariums" By Jeffrey Kurtz., and it basically solidified my desire to keep a cool reef tank, and make it as close to a closed natural ecosystem as possible. I found Jaubert's method of Natural Nitrate Reduction the most fascinating.

"A complete biological filter, converting ammonia to nitrite, which is converted to nitrate (via aerobic bacteria), which is in turn converted to nitrogen (via anaerobic bacteria)". The nitrogen bubbles harmlessly to the surface.

So after some more research, I talk to my LFS guy, and ask him, anyone in town you know use a plenum?

His response; " a Whatem?"

So with no first hand knowledge i decided i could do it anyway since it was fairly straightforward. I got used 55g aquarium with stand, lights, crushed coral gravel, and an under gravel filter. The filter was perfect for a plenum because it had all the ingredients already. White egg-crate (why its called that is a mystery to me, being neither Egg shaped or Crate shaped), Some black nylon window screening, Some 1/2 inch PVC elbows, and of course the gravel.

I set it all up with a powerhead for water movement and let it cycle. Being on a pretty tight budget, I had to slowly acumulate rocks and livestock, and after a few months i had a problem. An anemone died while I was away for a few days, So i also lost my cleaner shrimp and some snails and hermits. This was a result of not having a skimmer. Luckily i got a big Corallife skimmer for my birthday the very next month and the water quality has never been better. I think a skimmer is essential with a plenum, But don't worry if you like some detritus in your water for filter feeders. I have extraordinary growth of all types of polycheates in my tank, because there is only the skimmer intake cover and a small sponge on my powerhead for mechanical filtration.


That is all I have needed at a great cost savings because I Don't need an expensive Canister filter.

This method of filtration could be used with a Canister filter of course, but i am personally against them. I know some people are concerned with water clarity. I am planning a wet/dry sump/fuge to add more bio filtration and some Planktonic detritus. I think once I get some leathers and SPS in there they will benefit from the diversity of food items, because at night i can look with a flash light and watch 'Pods skittering around.

There are many ways to set a plenum up, but for mine i left some areas where room light could get in, and i varied the substrate thickness.







Some methods favor two layers, gravel and sand, separated by more screening, but i mixed my coral gravel and carib sea live sand. I think as a result of this i have a more plentiful and diverse ecosystem, with about 4 species of bristle worm, a large mysis population, 7 species of polycheate worm,

Worm growth


about 40-60 spontaneous baby astrea snails, and at least 12 different species of copepod/ampipod. And all that Is hitchhikers who have found happy homes. Of course i have livestock i have bought. A few corals and fish. The list is a humbug damsel about 3 years old, a yellowtailed blue damsel, an Ocellaris clown, skunk cleaner shrimp, 2 types of mushroom, a decorator crab, and 6 hermits. Also a fat and happy Mandarin,

Barmitzfah the Dragonet


who i have never got to eat any prepared food, and has been in my tank for about 5 months now. There is no chance of him depleting the pods, because of the amount of gravel they inhabit.
Recently I have noticed sponges growing in crevices and underneath some rocks. They will benefit from the nutrient rich waters resulting from the plenum as well

Regarding maintenance;
A plenum seems to me to be one of the most maintenance free systems, in comparison to a sump with a DSB or a canister filter. I do not have any return hoses to worry about, or filter media to buy and replace. No possibility of a check valve leaking or intakes sucking up animals. I just clean my skimmer when it needs it and wash the sponge on my one lonely powerhead once a week or so. No need to vacuum the substrate because the worms and mysis drag any fish waste or food waste down under to be devoured. it has been running for 8 months now without a single water change, only topping up with fresh water or adding salt if the density gets below 1.22 from salt creep.

There is some information that if your substrate becomes too tightly packed, it can create small toxic pockets of gases, but i think with adequate water movement and enough sand sifting organisms, you should not have this problem. Also there is a method of Occasionally draining out some of the plenum water with a straw or small pump, but i belive that to be needless. Needless because its the natural cycle for the sand sifter bugs to exchange the water by digging burrows and such.

I would like to hear from people about their plenums, failed or successful, and perhaps someone with a non Plenum system can comment on their biodiversity of non-purchased creatures to show a comparison.

Thanks for reading,
please reply with your thoughts
Ken (argan)

 

Argan,
I also run a plenum but I did things differently. I also dug into the Jaubert methods and articles as well as others penned by Shimkek, Sprung and others in regards to sand beds and "natural" filtration. I set up my plenum w/ a DSB BUT I used a much smaller grade sand and NO coarse rubble or the like. The research I read all pointed towards a small grade that WILL compact a little allowing very little O2 to enter the deeper layers. I set mine up like you, egg crate, screen, sand, screen and more sand, the layer of sand sandwiched between the screen prevents the "diggers" from disturbing the anoxic areas. I have my DSB/plenum as my 'fuge so there is also chaeto and caulerpa in the tank so it is also rich in bethnic inverts and their larvae.
In regards to your statement about sandsifters and pockets of gas, the main purpose of a "plenum" or DSB is to NOT have sandsifters and the pockets of gas should not be of issue as they will not be released by the "diggers". Also, on that note much of the whole gas pocket thing has really become a wive's tale per se, and a horror story against DSBs.
A note on the "nutrient" rich water Ken, I personally wouldn't advocate not doing W/Cs or having nutrient rich water UNLESS you were trying to replicate more of a lagoonal tank or expirementing with softie husbandry or the like. Coral reefs are typically VERY nutrient poor when it comes to nitrogeneous wastes and tanks can and will eventually crash if continuously kept with a high nutrient level. So, I'm not trying to rag or scold you, just giving you a friendly warning that your stony corals will most likely grow slowly and algae outbreaks could be right around the corner.
Otherwise, to all you folks first learning about plenums here, they can be VERY effective filtration and help create biodiversity in a tank BUT they must be kept properly, so before you rush off to build one of for that matter rush off to "knock" them, do your research and find out how effective they can be.
Thanks argon for starting the thread!!
Good luck all!!