I'll try!
Hi,
First, I'm going to speak in extremely non-scientific terms. It makes the same point and runs less a chance of confusion - Understanding is the goal here, not impressive language!
So, in simple terms: I'd like to sort of establish two types of detritus, probably not "technically" correct, but at least understandable from where I see your concern.
Lets call the first detritus "uneaten food". Now, be it a CC bed, or DSB, this always has a chance to get eaten by attentive crabs, although it is certainly logical that if it is
not worked down into a CC bed it is easier to get eaten by not only crabs, but also fish. So, your reasoning is indeed correct. It
is easier for food to get eaten in a "second pass" if it is laying out in the open, or sitting in a ledge of rock. The deeper it gets into the CC, the greater the chance of it eroding into what is the second type of "detritus."
We'll call that
decayed food and fish poop.
This is the stuff that hasn't made it into the food chain, or in fact
has made it all the
way through the food chain.
Let's consider this to be the group that will "turn into nitrates." This will be what we know as the last stage of "ammonia-nitrite-nitrate".
You are again correct in that a DSB has been proven far more efficient at breaking this nitrate down into a nitrate gas. The anaerbic layers of a DSB are much closer to the surface of the detritus, and it does what we simpletons like to refer as "sucking down" the detritus into this no-oxygen layer to convert it to the nitrate gas.
SO, do I suggest swapping out a CC bed in favor of sand? I certainly do recommend to all new tanks, and I'm even for swapping it out of established tanks - for no other reason than ease of maintenance. I'm not saying "one method is better than the other," although I won't be totally spineless.
I'll say one is certainly
easier than the other!
I also believe it establishes a very stable ecosystem, able to handle pretty impressive decay without a rise in nitrates.
I'm going to "paste" an article I wrote. This was in response to a similar discussion in which someone suggested I "write out a method" of what I was talking about - "stirring" the sandbed. Here she goes!
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Hi all:
I was mentioning a “worry-fix” in an online thread about sandbeds. The thread voiced concern about the “buildup” of toxic gases within the sandbed. Whether the concern is valid or not is not what this is about. This is about NOT worrying whether you will have a buildup of gases in your own tank.
To accomplish? Well, I prefer a 3/4" tube (the best types are the clear ones which can often be found right in the fish department of a big lfs to slide over fluorescent lights tubes). Think of it as a type of "precision" drilling method. You would first insert the tube down through the water and straight to the bottom of the sandbed - ALL the way to the bottom of the tank. Then, the smallest diameter rod or dowel can be inserted through the tube. You can then rotate the smaller dowel inserted through the large diameter tube and poke/prod until you've sufficiently "stirred up" that portion of the sandbed into which the larger tube has been inserted. A rigid hollow tube can even be used in the larger tube, and you could lightly blow through it or use a small air pump to aerate that portion of the sandbed into which you’ve inserted the larger tube.
This keeps the slurry confined to an exacting diameter of the sandbed - with absolutely no detrimental effects to the rest of the sandbed/tank. It accomplishes complete "stirring/mixing" of just that portion of the sandbed you are stirring. Of course, the amount of the sandbed that you work on should be proportional to the surface area of the sandbed itself. In other words, you wouldn't "drill" any more than 10% of the surface area at any one "operation" just to be safe. I always like to err on the side of caution, so perhaps a person could stir up the complete sandbed with no problems. That's not what this procedure is for, however. It is designed for that person who is concerned with the so-called "buildup" of gases in their sandbed and who doesn't want to fret about it. I personally don't lay any belief to a sandbed "self-destructing" if it is not stirred. I have not experienced it, and I don't believe my "drilling" process is a mandatory part of any maintenance procedure. I must allow such a disclaimer! LOL. It is, however, a process for those who might be concerned, or who are experiencing any sort of "crusting" on the surface of their sandbed. Some folks want a worry-free "fix" to some of the "dire warnings" mentioned by the "sandbed doomsayers" lol!! This would be just the procedure to "relieve" a sandbed of such death-threats. Again, I don't believe everyone should rush out and do this, and am not suggesting that anyone NEEDS to do this for a healthy sandbed. This is just a procedure to counter any worries about insufficient gas expense in a DSB (deep sandbed).
NOTE: This basically is a procedures which "aerates" the sandbed, and as we need our anoxic areas with no oxygen to process nitrates, one shouldn't go about "drilling" their whole sandbed in any sort of frenzy. This is why I again stress that 10% poses absolutely zero problem to the functioning of the sandbed and the nitrates it processes. So, the question might be: How OFTEN can I do this? Well, again I like to be absolutely sure, and 10% rotated once a month through the sandbed is more than safe.
Again, this might be an absolutely unnecessary "fix" to a problem that may not even exist. Some folks, however, do want some sort of "insurance" against all the dire warnings a few folks have mentioned about this so-called "death" of a DSB. This clearly “disrupts” any buildup without disrupting any majority of the functioning sandbed.
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I think the sandbed swap is outlined here in the archives somewhere, but it is a method which really holds your hand through the process. I encourage you to
NOT take any shortcuts. We've done this a lot, and even when we think we are "experienced enough" to not keep a printout at hand... we've invariably screwed up!
So, even if you
think your sandbed might be "building up" too much "detritus" because you don't have enough critters, you can always "maintain" it ever now and then with the stirring method outlined above. I'd like to again stress that I am not establishing any sort of "timeline" or "required maintenance" for a DSB.
The above just puts to rest any
QUESTIONS of it building up. A lot of folks were worried that their sandbed might be building up. There were things like "Old Tank Syndrome" being tossed about. Well, by the above stirring, you can logically see that there is
no possibility of a sandbed "building up" and getting ready to "destroy" your tank.
As for seeding it, I covered that in the Sandbed Swap article. Again, I don't make claims as to "necessity" just that it does fulfill that niche.
I've seeded tanks with nothing but live rock and had no problems. I've also added diverse sand from other tanks to see if I got "more diverse." Not to my naked eye, although I'm sure it's one of those things that could "only help."
Well, hope this helps out a bit.
