Bob replies...

Dear Prateek,

Thanks for your email, and I appreciate your courtesy and all the "Sir's" but they aren't needed, and "Hi Bob" will do nicely.

And I should add you have many very good questions and question 1 is especially interesting as you mention a subject rarely discussed, and that is the product "glycocalyx." This is a carbohydrate-rich cell coat on the external side of the plasma membrane of most eukaryotic cells. This includes animals, plants, and fungi, however 'not' bacteria or algae. If there were a fungi in the sand environment, there may be a type of mat created if they proliferate. Yet, the sand particles would not bind together, but the fungi may hold on to the sand particles. However, this is one of those situations similar to exceeding the speed of light. Not that anything is impossible, but it's the degree of probability that needs to be considered, and the possibility of a glycocalyx mat in an aquarium is an "extremely" remote possibility! However, this is not to say that sand clumping does not happen, whether in plenum systems or even those with beds directly on the aquarium bottom. Calcium precipitation and/or very fast forming colonies of bacteria cause this clumping effect, and due diligence is required so that it does not interfere with diffusion..

And its incorrect to assume there is no bioturbation by infauna. Yes, the diffusion process is of course more reliable than infauna, however, they will normally become part of the processes in the sandbed. And their activities for the most part are simply 'pluses' for the system.

As for question two, a screen between sand layers will not stop very tiny animals from entering the area under the screen. They are very small, such as copepods and or what I term "Meiofauna," which actually benefit bed processes. However, if it were a very large bristle worm, i.e., 12 inches, or another type of large digging animal then yes there would be an impact to plenum efficiency if there were no screen. And if the plenum were that affected, it simply would no longer work correctly and the entire sandbed and plenum pace would act no different than a sandbed directly on the aquarium bottom!

In question three, you mention 'stirring' the sand with a knife when surveying the bed for clumping. That's an incorrect approach, as you're not stirring the sand with the knife blade, but simply running it through the bed in a criss-cross fashion. And that's the reason for using a dull/rounded knife blade, such as a butter knife (my wife wondered where ours went for years!) so the plenum screen will not be damaged. And you're only doing it once per month. If you find any areas beginning to clump, simply break it up with your fingers. If you do that monthly, you'll be able to find any area beginning to clump, and prevent it from becoming larger. This works very well as I have kept many plenum systems, and this method has always been reliable. Its that simple!

And don't worry about the slight disturbance at the plenum/grid screen, as that won't be a problem. And as for releasing plenum water into the bulk water by running the blunt knife all the way down to the plenum screen, that will not happen. Remember, you're simply making an extremely narrow incision in the sand, one which refills the gap made by the thin blade immediately after passing through it.

I often see question four asking about the addition of small creatures to the sandbed. Actually, the small worms and crustaceans that normally accrue in sandbeds are actually a big plus for all type sandbeds including the plenum bed. They feed upon detritus, besides bacteria, and help diffusion in their own small way. Only much larger creatures such as gobies, very large bristle worms, etc., would be a problem, and only if they create much disturbance in the bed. And you'll find these small critters will develop on their own after introducing live rock into the aquarium. Therefore, purchasing someone else's "waste products" as I've heard these 'kits' called is not something I generally recommend.

Question five is also something I see quite often. As for what is said about the product, it's correct, however I see a slightly larger grain size a better way to go after years of experimentation. Yes, the 1 - 2 mm sand will work, at least for a while, however, some of the smaller grains may clog the screen, as they are quite angular in shape. Because of that and that 2 - 5 mm grain size material helps keep the diffusion processes/channels operating even when detritus collects and/or sandbed maintenance is lacking, I am of the opinion the larger grain size is a far better choice for "long-term" success!

As for the smaller the grain size the more bacteria, that's a fallacy when it comes to sandbeds in aquaria. Even though there are more sand grains resulting in greater total surface area and therefore more microbes it's of no value when one thinks of overall system balance. Small grains pack together very tightly and the space between them, porewater, is greatly reduced. When that happens, anoxic conditions as defined in my previous writings are restricted to an extremely shallow depth just below the upper oxic area. Important microbial processes, i.e., mineralization, nitrification and destructive denitrification all have greatly reduced volumes because there is less penetration of oxygen. The remainder of the bed then becomes anaerobic (also defined in my previous writings) and is where Ammonification, a form of denitrification that only reduces nitrate back to ammonium becomes prevalent. Basically it's more microbes but not the right 'class' of microbes such as facultative anaerobic heterotrophs instead of obligate anaerobic heterotrophs. And in such cases, bioturbation, i.e., increased infauna irrigation and transport, become a more dependent way of life than diffusion. And if this were my aquarium, one type of sand, probably crushed coral, with a four inch (10 cm) bed of 2 - 4 mm sand and no dividing screen would be the way I would go. .

As for question six, you mention shell particles, however don't mention their size. If they were flat-sided pieces above approximately 5 mm, I would prefer they not be used. And yes, said shaped and sized particles will trap some detritus, and also interfere with diffusion. So, if sand containing these particles is going to be used, recommend sifting the sand through a screen of the appropriate mesh size to remove these 'shell' particles.

In question seven you ask about inoculating dead sand with live sand. Actually, when receiving what is termed 'live sand' there's no telling what microbe class is really where in it when you receive it. Probably all the different types have gone dormant and will stay this way as long as they are damp. Therefore, what you receive has all types of dormant bacteria and the best in my opinion is to spread that live sand throughout the entire new bed so that some proper classes of bacteria are in all areas, not just one area. This would then enable a quicker start of all areas of the bed.

As for purchasing live sand in question eight and that of your location, I can not say whom to contact. Checkout the various websites, but delivery price to your area will probably be far too much. I suggest looking in your local area for the common crushed coral and simply using that for the plenum bed. And use it throughout the entire bed, as separate layers of different size sand is not needed.

In your last question, the keeping of triggerfish and sea stars does not mean you need a dividing screen. Yet, the species you decide on should be resolved before you set up the system, as some may be troublesome/diggers. And as for Scott's book, an excellent addition to anyone's library. and have it and many of his other books reviewed on my website.

Hope this answers your questions, and good luck with your studies.

Cheers,

Bob