Saltcorner
By Bob Goemans
By Bob Goemans
Dear Bob,
First of all, thank you for the responses to my emails in the past. You should be commended for the efforts you put into the marine aquarium hobby. You are very unselfish with your time, and I think I've emailed you three times over the past five years and have gotten a great response each time. I don't know how you do it.
I would like to know if there has been any more study on the substrate size used in the plenum system. What I would like to do is use the recommended size for the 1st layer of substrate. On top of that I would like to put 2 layers of window screen and use oolith sand on top for the upper layer. Is this combination possible and still retain the integrity of the plenum system? My reasoning behind it is, honestly, I prefer the look of oolith sand but also believe that less detritus would get caught up in the sand as opposed to the larger grains. From what I have read my understanding is that a size of 1 - 2 mm used throughout the system is ideal. Is that correct?
I fully believe that for the plenum to work properly it needs to be set up properly. From my experiences those that have had problems with the system seem to have deviated in one way or another. My first plenum was set up per the instructions from your articles in the Marine Fish Monthly magazine. I have since then read your book and another persons book. I really wish the other person would spend less time talking about why everyone else is wrong and more about how his ideas work. I belong to several forums on the web and am a little overwhelmed by all the info out there, some good but mostly bad (in my opinion).
I have never done a deep sand bed but from what I have read, it seems to work, but if something goes wrong or you need to move the tank, look out. I also do not feel that it has been proven long term. I also do not feel it would be as efficient as a plenum. Do you have any insight you could offer me? I currently have my tank moved into a 100 gallon vat in the basement (thanks to your info on moving a tank) and will be setting up my new 200 gallon tank once the living room is remodeled (part of the deal made to get a larger tank). So I have the opportunity to set up a new system and would like to do so with the most up to date information available.
Thank you so much for your time.
Mark Szwabinsky
Hi Mark,
Thank you for your kind words. I enjoy this hobby and always had a passion for learning more. I see from your letter that you're a past reader of Marine Fish Monthly magazine, which went out of business due to the Editor's poor health. My 'Salt Corner' column in that magazine had 178 straight monthly articles without ever missing one month! Now in my retirement years I'm still spending a lot of time to helping others along with building an educational website where hobbyists can get honest, professional, and up-to-date information.
As for your question on substrate particle size for plenum use, there has been much study over the past decade on what size sand grain is the best for diffusion, which is the main nutrient transport method in substrate. The result is that a grain size of 2 - 4 mm is the best. Yes, the 1 - 2 mm size is still usable, however, it has been found that a slightly larger size material insures diffusion will remain achievable even when system maintenance lags. And, I should note that all substrate should be the same physical size, i.e., 2 - 4 mm. Where the notion started that different size sand grains should be used is not clear, however, it serves no useful purpose.
There's no doubt fine sand can help lessen the penetration of detritus, however, it also reduces the degree of diffusion/oxygen penetration. And that would then put more emphases on the need for infauna to ply the depths of the bed, which is the case in deep sandbeds directly on the aquarium bottom. Keep in mind diffusion/oxygen penetration is of great importance and the key to plenum efficiency. Even with 2 - 4 mm sand grains, some detritus penetration is not of major concern (actually a food supply for some of its bacteria) if one performs their system maintenance as they should. And if you don't like the look of some detritus along the side panels of the aquarium, leave a half inch space between the edge of the plenum grid and the side of the aquarium. Then, as needed, simply run a thin wooden/plastic rod (I use a chop-stick) between the grid and side panels to stir the gravel. This does not, even in the slightest, affect the efficiency of the overall plenum system and the sand will always look clean.
As for oolitic sand, a term used to describe the shape of this particular structured sand particle, it's shaped differently than the more pure aragonite mineral. It is basically round from being tumbled by wave action, whereas aragonite is an irregular shaped 'mined' product. And, just as important, aragonite is a softer more porous mineral and more easily dissolved than oolitic sand. Oolitic sand consists of concentric layers (like an onion) of calcium carbonate that surround tiny remains of coral skeleton material, invertebrate shell, calcareous Halimeda algae (basically the aragonite mineral), and tiny amounts of calcite. And because of its smooth rounded shape, sites for bacteria adhesions are not as good as they are with courser, more angular grained material. I would think more about your selection of substrate. And, if it were my system, I would go with one size sand material and would eliminate the dividing screen if at all possible if no major digging animals will be in the system. As for two layers of screening material, whether on the grid or as a dividing screen, consider that the maximum on the grid and only one layer as a dividing screen.
Without a doubt, the plenum system has proven to be very successful, and that it is best established using the very simple setup instructions that apply to it. When I was speaking in Chicago last year I mentioned that any type system, e.g., undergravel, shallow sandbed, deep sandbed, algae scrubber, no sandbed, plenum, or Berlin system can be successful (I've had them all), and that their success is simply related to the level of maintenance each receives. However, I've found that when the plenum method is used, it has resulted in far better water quality because of its more efficient biological processes.
Hope this helps and keep me posted.
Bob
