DSB controversy...spanning the boards.

[JeremyR]

Galleon:

Out of curiosity, how much real world experience with sandbeds do you have in closed systems and how much of what you are saying is theoretical or based on other peoples observations? For every person you dig up who has crashed a tank and blames it on his DSB, I bet a Len can be dug up who has one going on 9 years. I'm not a DSB fanatic by any means, but from your own admission other places you are not a "hobbyist" and I wonder what your actual experience with the sandbeds in question is.

 

[liquid]

So if you were to give a recommendation to a person on sandbeds, what exactly would it be (sandbed depth/particlesize/etc)?

Also since this thread has come up I might as well point people to our Sandbed Survey: http://reefs.org/GBSurvey/surveyq.php?s ... df7d116e46



Shane

 

[Anonymous]

Something can't go to nothing, and it isn't removed by skimming or detritovores or N2 offgassing by a longshot.

Do we know this for sure? I never siphon my sand or rock, and have no observable detritus on or in the sand, although I suppose some is there. Pound for pound I'm sure I remove more skimmate and macroalgae than I put fishfood into the system, so I don't really see why detritus has to be building up.

 

[Anonymous]

Liquid, what I use at the lab is preferrably bare bottom, so detritus can easily be siphoned off. If I put in shallow sandbeds, they would be things like Seaflor special grade, less porous than crushed coral and thus less of a detritus trap (make it more difficult to siphon out).

Dan, The amount of skimmate you remove is not really comparable to how much you feed as far as direct observation goes. Detritus is just something that forms. I promise you have detritus settled in your sand, and it will build up. I use very overkill skimming and high flow, and I don't have fish to feed, and detritus still forms and settles.

Be back in a bit, lunchtime...

 

[Len]

Just how fine of a sand is reccomended for a DSB? Should I stir my sand more often? Really churn it up?

0.2-1.5mm is a good range. Caribsea's Sugar-sized, special grade, and oolitc sand are good mixes IME. You can mix the sand thoroughly if you're using different particulate sizes, but they'll eventually settle on their own. Don't churn up the sandbed once established.

Now we return you to your regularly scheduled debate .....

 

[wade1]

I'm wondering if we are leaving too much biology out of this discussion in relation to the cycling of nutrients. If we have well populated, diverse sandbeds, these nutrients aren't actually 'sinking' into the sand at all. They are being consumed and migrated by the detritivores, which put effort into reproduction and the cycle continues by feeding our filter feeding friends. I know that a good portion of the detritus is probably being consumed by fungi and bacteria, but even they release what they don't consume as water soluble waste. Which means its back into the water column...

I don't agree that sandbeds are long term sinks for "nutrients" or those elements which organisms need in high quantity (N, P, C)... they may be in higher density in a sandbed in total, but if you removed the live organisms, I doubt you'd find significant amounts. That said, there will be a buildup of some compounds... mostly organic compounds that are extremely stable. Luckily, nature doesn't produce too many of those. Humans certainly do though...

Also, sand being inorganic means that it doesn't serve as a lipophilic fraction for binding organics readily. So, the turnover of sand by our "diverse and high density" detritivores should continuously release more of those organics into the water column. (Hence the strong need for skimming and activated carbon usage)

Just my theories...

Wade

 

[Len]

What I'm unclear about is why detritus acculumation in the substrate is such a feared occurance. If the organic and inorganic material is being sequestered, what's the concern? Even if it's leeching some undesirable elements and compounds back into solution, is it really to a degree that anyone should be alarmed? After all, there are many mechanisms for export of said elements and compounds, some natural (there's more processes then just the N cycle) and some artificial (skimmers, water changes, chemical absorbants, etc.).

Every time I hear DSBs regarded as ticking time bombs, I keep picturing my substrate all of a sudden exploding and releasing everything back into the water column.

 

[Anonymous]

Yeah, I just don't see it as problem, nor have I experienced it as a problem. I feed my tank VERY heavily, and when I stir the bed thre is no observable detritus.
I just don't buy the nutrient sink thing, and all empirical data that I've gleaned doesn't support this notion either.
Jim

 

[liquid]

You know, I have full access to ashing ovens where I work. If I'd get core samples of peoples' sandbeds, I could give a relative idea of how much organic detritus is bound up in the substrates. I couldn't tell you any more than a percentage of organics, but it'd be interesting data none the less. If this is of interest to anyone, fire me off an email or something. Maybe something could be written up for AAOLM on this. I've always wondered how much krud was in my sandbed but I've never taken the time to ash any of it.

Thoughts?

Shane

 

[Anonymous]

<shrug> I've said it once and I'll probably say it again (regardless of whether I understand why people put these things in their tanks or not): To each their own and I hope it keeps working for you.

 

[Len]

I'd love to know to. I'd send you samples of my tank and at least 2 other people's. For meaningful analysis, we'd have to get some info on each submission such as tank size, age, feeding habits, livestock, substrate composition, etc.

I think this would be really cool to find out.

 

[wade1]

If I'd get core samples of peoples' sandbeds, I could give a relative idea of how much organic detritus is bound up in the substrates.

Well, it will tell you an organic % by weight, but it won't tell you anything about if those organics came from living animals/bacteria or not. Could be an interesting comparison study though... especially if you managed to get some sand from some florida reefs to do comparisons.

Wade

 

[liquid]

Yeah it wouldn't do much to determine where the organics came from but I don't see any way of removing bacteria and microcritters from the equation. I guess I could soak a control in some waterchange water for a month and let it get good and populated by bacteria and see what happens...

Shane

 

[Anonymous]

<can't leave it alone>

regardless of whether I understand why people put these things in their tanks or not

Well, I'm sure you know this already- but you understand/agree with the use of live rock as a matrix for bacteria, correct? The DSB is exactly the same thing, but more surface area, more efficient....

 

[Anonymous]

Shane, that would be awesome!

Wade, sand from reefs has already been analyzed in this light, check out Sorokin: less than 1% of the sand benthos (not including bacterial biomass) on high energy reef areas is organic carbon.

 

[Len]

<shrug> I've said it once and I'll probably say it again (regardless of whether I understand why people put these things in their tanks or not): To each their own and I hope it keeps working for you.

You wanted a debate, so here you have it

The reason why I have a DSB is simple:
1) DSBs increase the biological diversification of my tank by providing additional and distinct habitats. Rarely is this a bad thing.
2) DSB is a good denitrifier.
3) Sandbeds look nice to me

I haven't encountered any reasons not to, but I'd love to hear arguments why I shouldn't. I'm open to different opinions, experiences, and theories.

 

[liquid]

Well heck, let me take a core sample quick of my sandbed and see if it's even a viable thing to try. I'll dry it out in a forced air oven overnight and then ash it tomorrow. I'll post the results here.

Shane

 

[Anonymous]

Galleon,

do you have some convincing evidence that proves a DSB cannot handle the loads imposed on them when properly utilizing other export methods(such as skimmers, refugiums, carbon, etc)?

as i said, i am completely open to hearing your thoughts on this. but so far all i hear is you stating very simply that it (DSB) cannot break down the intended load of detritus. i would like a little explanation as to why it cannot.

i had a six year old bed in my last tank and when breaking it down there was a nasty smell and plenty of organics within the bed. i assume the bed had been that way for some time. i would also presume that if it became overloaded to a degree with foul organics that the result would be problematic algae.
this seems to be the case for some on the RC thread, explained as a constant problem for them when using a DSB. wouldn't it seem likely that those systems using a DSB without the problematic algae would not be fitting to your sink analogy?

 

[wade1]

Digging up the literature is the only place to start and finding values would help alot. But, using current samples would still be a very good idea to validate or show the variation for our sampling.

One other consideration would be to pass the sand thru a filter once its been recieved, that allows nothing larger than a grain of araganite thru (getting a single large worm for example would cause issues).

Wade

 

[liquid]

Ok, I couldn't take a core sample like I hoped w/ a 1/2" PVC pipe. All the sand fell right out so I ended up scooping about 2 fluid oz of substrate from the top 1" of my sandbed. I would have liked to go all the way to the bottom, but it wasn't possible due to space. I'll pass it thru a coarse filter to remove any large worms and then I'll get it going. Just looking at what I dug up, it looks like a muddy mess. Blek!

Shane