Sand bed thoughts

[SuperFudge]

Why would it be recommended to change all or part of it out at all, if it could cope all that the tank produces for waste ?.....because it just doesnt.

If the sandbed werent there or just minimal, the skimmer or other filtration would have a chance to take up the extra,and siphoning of detritus could be handled easily if any remained on the bottom.

There is no question, it is a sink.

One should also consider is that the sandbed does contain huge amounts of life...could part of the reason for problems stem from die off of some of this life ?

I sort of look at it like a time bomb sitting under my rock waiting to go off.

[Troy F]

The plankton we're referring to when discussing the DSB is the benthic faunas' larvae, sperm and eggs etc. I kind of thought with the area of discussion we were in, it would be obvious. My apologies.

I'm not sure I completely agree with the statement you've made concerning a properly sized DSB. What are you using as an indicator that a DSB can handle "ALL" detritus?

[MitchM]

Thanks, guys. I guess I never really considered that the volume of larvae, eggs, ect from a DSB was that significant.
I don't know how to effectively "size" a DSB, but I do have it in my mind that given a large enough surface area, and the proper depth, of course, that a DSB should be able to handle all naturally occurring detritus material. (which excludes any extra chemicals that would come from our artificial salt, additive over dosing and processed food)
My new set up here has a 180g sump/refugium that has a 4 or 5 inch DSB. I've really noticed a difference with detritus accumulation, or the lack of, compared to the bare tank sump set up I had before. The sandbed in the sump/refugium has NO detritus building up on the pumps, floor ect. I can't help think that if I had a big enough DSB, I could get rid of my skimmer.

Mitch

[christyf5]

I'll admit it. I'm a sheep. I first started my tank with a plenum because it sounded good at the time. When I moved up to a larger tank I was told a 4" DSB was the way to go. I guess I just go by the experiences of other people and nobody I talked to at the time had a bare bottomed tank. I kind of like the added glow of the white (well pseudo white in my case) sandbed. I also think it provides a home for a host of critters that wouldn't necessarily be around if I didn't have the sandbed. I also think that the DSB really should be recharged (or at least charged) with new critters (ie. sand exchanges from other tanks) fairly often. I would think that the critters in your tank can't necessarily handle ALL the detritus that the DSB receives.

Does anyone know exactly HOW the DSB becomes a sink for all the heavy metals and such (chemically I mean)?

When you say the DSB becomes exhausted after a few years, what exactly does that mean? What about it becomes exhausted?

Christy

[Aquattro]

Christy, both good questions. How does aragonite become a sink? Are toxins adsorbed?
What is exhausted?? Ca?

[Bob I]

Last night I asked a simple question, and Brad gave me a simple answer, which I appreciated. Now when I wanted to give a bit of a rebuttal (not an argument), the thread has really grown. But I still want to make a small point if allowed. The point was that given the small grain size of a typical sandbed, and each grain can be colonised by bacteria. You would need tons, and tons of rock to equal the area for bacteria to colonise. I hope that makes sense, as I am having a problem with the sentence structure.

In addition some time ago when I hung around Aquaria Central there was a thread about sandbeds where a guy really was upset, and told us the inherent danger of sandbeds crashing, and killing everything. The outcome of that discussion was that there was almost no anecdotal evidence of such a thing happening.

I myself have smaller tanks (the largest being a 50), and consequently I have moved sandbeds a number of times. The only time I noticed some H2S was when I had a six inch sandbed. Since that time I keep sandbeds down to four inches without any problems.

I hope I did not bore you with this.

[Diomedes]

Sinks? Sources...

The DSB is both a Source and a Sink. These are opposite terms used to denote things that either provide something or take something away. In nature the Mangrove swamps and Seagrass Flats act as a Sink for some of the nutrients produced by the highly productive reef, which is a nutrient Source. A properly set up aragonite DSB is a Source of natural minerals and buffers (Ca, Sr etc.), can be a Source of natural planktonic and larval prey items for filter feeders and corals. If there is a ton of rotting material in your DSB then it is a Source of phosphates and other nutrients that are released by fungi and bacteria. It is a Sink for Nitrate, meaning it absorbs Nitrates. I think a properly set up DSB is better than Live Rock at Denitrifying, but that doesn't mean it has to be in your display, under your lights, accumulating detritus. It can be a separate filtration component altogether, plumbed in line.
As far as DSB's accumulating toxins...Do you mean H2S or Heavy metals?
Aragonite is constantly dissolving so that would release the bonded heavy metals back into the water. H2S is not something I have experience with...It used to be a big concern when LR wasn't being used along with the meiofauna it imports.

Stephen

[Quinn]

i get what you're saying bob. the smaller the grain size, the more sand you have in a cubic inch, the more surface area there is, the more critters can live on the sand. the bags of SWC sand jon brought in has some absurd number on it, the exact space available, but it makes sense i guess. the same concept applies to bioballs.

i guess the one thing i can't figure out is, where is the sulphur from the hydrogen sulphide coming from? it's not organic waste, it's not in the water, it's not in the sand... or am i missing something. however it does make sense, that if you're going to have anoxic (is that the word) areas in the sand bed, then there has to be some other gas down there, and H2S makes as much sense as any, i suppose.

[Aquattro]

Sulpher is an element that is in most organic matter. Food contains sulpher in some form. It's everywhere!!