Temperature of a plenum-An Experimental Comparison of Sand..

[A. Iosue]

In the Dr. Robert Toonen and Christopher Wee article ´An Experimental Comparison of Sandbed and Plenum-Based Systems. Part 1,2: Controlled lab dosing experiments´ they just talk that the: "experiment was run in a temperature-controlled environmental chamber set to 25ºC (~77ºF) that... " in part 1 and "temperature and light fluctuated at natural rates." in part 2.

As new in saltwater hobbie I have read some article and found those guys trying to make things as Natural as they can, I like that.

The lot of controversy found in this topic confuses me and obliges to read something more serious articles as the Dr. Tooner and Wee one. They says the experiment is a "Controlled lab dosing experiments" but makes me think in the case of Plenum system that they did not look at some variables and perturbations. I want to know whats happening with the temperature at the sides, center inside, center outside the plenum after and before bacterias starts to work?, how plenum can interchange its filtration water in a good rate?, which is the moving rate of the mass of water in the center of the plenum? (at the sides would be find cause the heat interchange due to convection), if it doesnt move (water catched as in a bag), plenum and non-plenum are the same for me or plenum worse, those the anoxic catched water-bacterias in a plenum promote H2SO4? and IF I TRY TO INTERCHANGE THE TANK WATER WITH THE PLENUM WATER AT A NEAR OPTIMAL FLOW RATE (rate at which the bacterias can do good filtration), COULD IT SAY THAT PLENUM IS A GOOD SYSTEM???

Maybe those successfuls plenum systems have a perturbation not seen or not considerated importants as could be a source of heat under the tank.
If a lamp is placed under the tank and radiating its heat to the plenum across the glass, and heats one side of the plenum, the convection moves the water and exchanges the filtered with the unfiltered water faster. Perhaps they are not seing this!.

Well I want now to expose my idea.

The Idea is to place the plenum not in a flat, parallel or plain possition with the glass, instead inclined, shaping a triangle, I mean a plenum with variable height. Water with less temperature gets inside the plenum at its shorter side heihgt, performs the nutrient processing and gets out at the taller side. I am thinking in this cause the bacterias will produce heat while filtering and that heat gathers toward the taller side of the plenum forcing by convection the water flow. No external energy required.

My other idea is to cover up the center of the plenum leaving just the inside and outside of it to prevent heat losses and water coming out from the center without taking good contact with all the bacterias.

Is mandatory know the external heat around the tank and sediments (external influences as heat sources, etc.), the heat around the place where the plenum will be arranged being assure that the shorter side heihgt of it is not hotter that the other side so convection will not occurs or occurs in a reverse way.

I would like to know your opinion about this plenum system and also I want to beg you pardon for not to be more explicit cause English is not my natural language, I really want to expose a lot of more things.

Thanks to Dr. Robert Toonen and Christopher Wee.

A. Iosue.

 

[Biogeek]

Hi A. Iosue.

Your question is one that we wondered about as well, which is why we did the comparison between the controlled lab experiments in both controlled lab conditions without any animals or perterbations, and under natural conditions with both natural infauna and reef organisms. We reasoned that if factors such as disturbance, temperature, lighting, or organisms played a role in the overall functioning of the plenum, then we should see some difference between the results of the trials run under controlled lab experiments and those run under natural conditions with live organisms. There are always a range of other factors that may play a role, and are outside the scope of any experiment, but we did the best we could in this comparison. However, I would argue that if the unknown factor (such as a lamp under the tank) that makes a plenum more effeicient than a sandbed is missed in our experiment, it would probably be missed by most people setting one up at home as well. At least as they are used today, our experiments show no difference between the plenum and no plenum treatments, so we see no reason to go to the trouble of including one in our tanks.

You ask COULD IT SAY THAT PLENUM IS A GOOD SYSTEM? Our results say yes - a plenum system is every bit as effective as a deep sandbed system, because both function equally well. Is it possible that another design may make a difference in the efficiency of the plenum? Sure, but I have also written a review article on the biology and theory behind these systems (http://www.seabay.org/art_plenums_part1.htm and http://www.seabay.org/art_plenums_part2.htm) that outlines my criticisms of the plenum system. Somehow people seem to think that an empty space increases the number of bacteria present, but bacteria grow in much higher densities on the surface of small sand particles in a sandbed than they do in the open water of a void space. The same thing is happening in a sandbed of sufficient depth as is happening in a plenum. As far as I can see from the biology outlined in the articles above, and the experiment we recently published, the activity happening within the void space is so small compared to that in the sediments themselves that is has no detectable effect on the overall health of the aquarium. Given that, I don't see much reason to go to the effort, time & expense to include one in my own tanks...

Aloha,
Rob

 

[delbeek]

Rob: I have run four systems with plenums and local live sand ranging in size from 175 gallons to 1400 gallons, some of these have been running since 1996. I have also set up four systems without plenums and local live sand ranging from 10 to 5000 gallons. What I have noticed is that all the systems without plenums invariably develop grey sand just below the top layer whereas the plenum systems have not. To me this is a significant difference between the two systems and tells me the plenum DOES have an effect on the sand bed. How would you explain these differing observations?

Aloha!
Charles

 

[pacemaker]

Dr. Toonen,

I'm happy that somebody actually took the time and energy to apply a "scientific method" to this topic rather than anecdotal observation.

I do have several concerns regarding deep sand beds (DSB) +/- plenums.

1) From all that I've read, I agree there does not appear to be any benefit to a plenum with a DSB, at least initially. The benefit seems to come down the road years later when the DSB is mature and helps reduce hydrogen sulfide release. How, who knows? Maybe the plenum acts to increase the surface area (expose the lower strata) of a local area that may have collapsed within the DSB and is now anoxic. Your study was very interesting but only carried out for 111 days. It would beneficial to this subject to see some long term studies...

2) People keep talking about "water motion" through the DSB/plenum. While water motion IS apparent ABOVE the DSB, has anybody actually demonstrated water motion through a DSB? Aside from an undergravel filter, how would water move through a DSB when there is no pressure gradient? I believe diffussion (similar to what happens at the molecular level with cell walls) would be a more appropriate term for the exchange of molecules through a DSB. And yes there would be a chemical gradient present to drive the diffussion process.
Diffussion may explain why the deep course gravel fared better than the deep fine gravel, and likewise, the fine shallow fared better than the shallow course gravel. I would like to see an experiment that demonstrates whether "flow" vs "diffussion" is predominent.

3) Proposed experiments:
Tanks with DSB (course vs fine, shallow vs deep, plenum vs no plenum).
Let all tanks settle and develop over 3 months. Then draw water samples weekly from 1) surface, 2) immediately above the gravel, 3) from 1/3 deep in the gravel, 4) from 2/3 deep into the gravel, and 5) from the bottom glass of the tanks.

Joe Pace

 

[delbeek]

For your point #2 ... it is called advection and is described in The Reef Aquarium volume 3 pp 261-265.

Aloha!
JCD