How Deep Should LiveSand be in a 55long?

[Bugotus]

Ive got 2.5 inches of LIve sand now and my clowns dig to the bottom glass. Tank is also cloudy and im having trouble clearing it up.

[gcvt]

For a deep sand bed to be beneficial, the general rule of thumb is a depth of 4-6 inches. Dr. Shimek has a very informative article on deep sand beds here: http://www.rshimek.com/reef/sediment.htm

[Ray Pollett]

gcvt,

I must have missed it in that article; could you show me where he says 4 - 6 inches? I saw where he said his was 4 inches.

I'm asking because no one seems to know where the 4 - 6 inch rule of thumb came from. Some test have shown it may not have to be that deep.

Ray

[a_free_bird73]

Well the 4 - 6 inches is not really a rule of thump but it kind of is.

It is based on experiments aimed at determining the oxgen concentration at various sand depths. Although I can't point you to the actual paper because I don't have the reference, I have read something along those lines several months ago.

The actual true depth depends on multiple factors including the grain size, the actual setup and water current and the types of organisms you have. All these factors influence the diffusion of oxgyen. because it is diffecult to determine the exact required depth without expensive and time consuming measurments, the accepted "rule of thump" is that if you have less than 2.5 inches, you are not likely to get any resonable level of denitrification. 4 inches is considered safe but if you have large grain size and a lot of disruptive organisms, then you may need the 6 inches.

You can test it but without equipments you could be looking at 3 months worth of experiments

[gcvt]

Sorry for the confusion - I didn't mean to imply that Dr. Ron says 4-6"; it's just a general rule of thumb in the hobby. As I understand it, 4" is the minimum you should put in medium to large tanks for the most effective biofiltration. And it's believed that once a sand bed gets deeper than 6" it begins to become less effective. Hope that clears things up a bit.

[FISH WHISPERER]

Hi,

2" sandbeds have worked in nano tanks (-10g) and Rob Toonen is actually gearing up a 48 tank experiment with different factors in groups of tanks. I personally think 2" sandbeds work fine in the nano tanks because they're not stocked with a whole ton of livestock - and those with corals usually provide all the uptake necessary to prevent a buildup of introduced food.

As for bigger tanks, we've run 3" in our trigger tank since Smitty and I set it up in early '99. Our full reef runs -4" (I'd say an actual average of 3").

However, the thing to note here is that we've got clownfish continually "digging" in Bugotus' tank. If we're trying to achieve anaerobic layers within the sandbed, that simply can't be accomplished with continual disruption - even if the sandbed were 6" and continually being disrupted to the bottom. Then, it would all be oxygenated and there'd be no conversion of nitrates to a gas which require these no/low oxygen layers.

Ron has never actually stated a requirement of 4-6". This is one of those "rule of thumbs" that have been passed down for years. It is certainly a safe rule of thumb, and it is probably the more common depth in many large tanks. As with so many things, what works gets passed down. Now, as more people are going with less depth, we are seeing that 6" is certainly not a requirement. But we have to have these tanks running for a number of years so we can disprove what would probably be the theory that these "thinner" sandbeds would be more prone to "buildup and crash." We're not seeing this, and after several years of successful -4" sandbeds it's safe to say that there's not a "deeper" requirement.

However... ;) I'm not about to assert 2" sandbeds as something I would recommend to someone starting out with a larger tank. Larger tanks usually have more fish which means more waste. I think 2" sandbeds handle the small load in a nano with a higher ratio of surface area-to-waste processing capability. I'm totally comfortable suggesting a 3" sandbed as a depth that works just fine in larger systems. I don't know if more depth would be needed in much larger systems with far less surface area of sandbed. But seeing as so many of us cover up the majority of our sandbed with rock - surface area doesn't even seem that critical in larger systems.

It's interesting to note that so much of the "waste" in our tanks doesn't even make it to the sandbed. We observe this when we take a turkey baster (or a powerhead, for a real show! ;) ) and "blow off" our live rock. There's a lot of detritus built up there.

As stated above, grain size is important. But 3" of Southdown is the norm in many tanks, and 2" is a good norm in many nano tanks. Normally stocked tanks have proven to show adequate conversion of nitrate buildups. I can say that substrate such as Special Grade Reef Sand (which is actually a smaller diameter crushed coral) is much larger and more coarse than regular playsand - and it failed miserably at keeping nitrates to a minimum at a 4" level in one of our systems years ago. Just as a comparison, the normal crushed coral so many of us once used ;) was shown to test 0 nitrates... at a depth of 22"!!! That tidbit comes from Rob Toonen.

The important thing, which we all pretty much know, is that the sandbed not be agitated down to the bottom of the tank. At any level this results in the prevention of anaerobic layers. If you have enough surface area, and the clowns are only digging in one area you'll have no problem. If they are disrupting too much of the sandbed - you'll lose the important layers we're talking about.

Our sandbeds our continually sifted, and because so many tanks have different inhabitants - I'm a little wary suggesting there is any "minimum" depth that would work for all tanks. We have to know what we have in our tanks, how much sandbed disruption is being posed as a threat. For example, a dusky jawfish can absolutely burrow to the bottom of a sandbed. Hopefully he finds a particular "burrow" which he calls home. Many wrasses, on the other hand can kick up a nasty hole in a variety of areas. Still, our sandbeds today seem to handle all this "disruption and sifting" quite well. :) With all the variety of critters people keep, the "4-6" rule has worked well. Perhaps a 2" bed would be insufficient in a larger system with more inhabitants (as there would be less surface area-to-waste being produced). Maybe 2" would work fine for some tanks and be insufficient in others. As with so many things - it's hard to establish one particular "level of order" for sandbeds (at least that's what I've come to believe). We have to take into account the amount of "disruption" to the sandbed and ensure we have enough surface area to maintain adequate anaerobic levels. Even small sifters which continually "turn" the tops of our sandbeds don't seem to have any major effect on the anaerobic capabilities of our systems.

Also, we have to keep in mind the amount of water flow (bringing oxygen) to the sandbed. Perhaps this might be a factor to consider? I don't know the "oxygen penetration" potential of a higher flow of water near the surface of sandbeds, but I've considered it to possibly being a factor in establishing a more shallow depth. Just some things to toss around. Cheers! :) :)

[kreblak]

Crushed coral will provide 0 nitrates at 22 inches?!?! That is just depressing. Monty, are there any tests showing the effects of a crushed coral layer on top of a sandbed? I set up a tank with about 3 inches of sand, and then another inch of crushed coral on top. I wanted the coral there for PH buffering, but now I'm wondering whether or not that was such a good idea. The system has run fine for 7 months, with the only real problem being that the cycle took forever. Nitrites didn't come down to zero until after 10 weeks!

Any thoughts?

[FISH WHISPERER]

I haven't tried 1" on top of a sandbed. I'm supposing that the success would depend upon the amount of detritus building up in the crushed coral (oxygenated, for sure) vs. the ability of the sandbed to suck down the buildup into the anaerobic layers. In a heavily fed tank, I would think the crushed coral could quickly become what we call a "nutrient sink" - notorius for leaching nitrates. Too many folks run regular sandbeds for there to be a need to buffer the pH with crushed coral. I don't think the benefits outweigh the potential buildup of nitrates, myself. We should get satisfactory pH levels from the salt mix itself. As for buffer, that should be tweaked if/as needed.

We direct the return from the main reef into a smaller container in the sump - this is an excellent place to "force" water flow through media without a threat of nutrient buildup; it's just too turbulent for anything to settle. I've been keeping an oyster shell in there to see how long it takes to break down. Oyster shells are one of the best natural "buffers" (even though they barely approach a low 8.0 in their ability to buffer pH - I think it's more in the higher 7's). It's certainly no "stand alone" way to buffer to the levels we need, and I'm just doing it to see how fast it erodes. If I wanted more rapid dispersion I'd hammer the shell up into smaller bits and put those in the container in the sump - that naturally seems like it would erode faster/buffer more efficiently.

But as for your tank, my ideas are: If it's working - it works! :) There's certainly a potential for a 1" crushed coral layer to become a nutrient sink, and then it's certainly possible for an appropriate load of unused nutrients to work their way to the sandbed. The concern would be if your sandbed gets "choked" by the top layer of crushed coral - but that doesn't seem to be an issue in your tank. It seems like you do a great job of monitoring your params, so you'd be the first to know if something starts to get out of whack. :)

[OrionGirl]

I don't know enough to comment on the dpeth of sand beds, but I don't think that the clowns digging into Bugotos's sand bed will result in the cloudy conditions, especially if there are not sky high nitrates.

In short--I think something other than DSB issues is the cause of the cloudiness.

[Bugotus]

Thanks to everyone who gave their 2 cents. I picked up on a lot from your suggestions. After a little tinkering with the sandbed depth I hope to see some positive results. Thanks again

[Ray Pollett]

Hi Monty,

It's because of the work Rob has done I asked about the 4-6 inches. He admits he can not fine it in any scientific work or articles; and has no idea where it came from.

a_free_bird73,

I would love to see the work you quote. I keep hearing about it but NO-ONE has been able produce the study or paper.

Best Wishes,
Ray

[wayne]

I note some comments above about debris making it into the sandbed or not. Well I don't think that's how the denitrafication part works, it's by acting on nitrate dissolved in the water. Decompositon to ammonia then nitrite is what happens to the 'solid stuff' we see, so it doesn't matter if the waste sits on the bottom, in the bottom or on the live rock as long as it's available to bacteria
Anaerobic bacteria get hold of the nitrate once it's dissolved in the water, and it reaches them by migrating from the aerobic water by processes of diffusion and sometimes by water entering (in aerobic form) with bioturbation, where it's rendered anaerobic. If there are any other processes that will help 'drive' water down into the anaerobic zone at the correct (slow) speed I'd be interested to know what they are, because I can't think of any that are common though I'm sure there are ways and means. They would be useful if easily achieved.
How deep does a bed need to be? I have only a little knowledge of resevoir engineering, but I would expect with smaller size grains you'd need less depth, and that's what the above seems to show. You should be able to see the anaerobic/aerobic boundary I believe (see the classic photo of Julian Sprungs jaubert aquarium). If you can't see anyting, don't assume it's there though it might be away from the edges. Obviously a living sand with burrowing critters will need more depth than an equivalent that's undisturbed, MAybe 4 -6 inches is the rule thats evolved as it's the one that works, but there's always a lag between rues of thumb and cutting edge. I can't think of why you'd need less depth in a nano, except the lack of big burrowers (maybe) and the lower biomass needing les denitrafication allowing for a smaller zone?
Any ideas on the effects of a plenum?

[Ray Pollett]

If I remember correctly. Rob's worked shows that a plenium does no better than a DSB and no plenium and can cause a lot more problems.

Ray

[wayne]

Actually Ray , to be a smartarse about it, if you don't think nitrates are a problem, then why bother at all, except for burrowing creatures comfort.
I was wondering if a plenum would affect water flow thro' the sand, and I think it might, but at a fiendishly low level by creating more of a 'nitrate gradient' (as it'll increase the nitrate free area and thus push diffusion)
b

[a_free_bird73]

Ray,

Check out this paper and possible contact the Author about the rest of the data. I think this summary does not actually show the oxygen concentration at the various depths but they definatly did measure it...

http://www.reefs.org/library/talklog/p_auger_081599.html

[Ray Pollett]

a_free_bird73,

Thank you for that very interesting paper. I really enjoyed reading it.

Wayne,

You might enjoy the paper a_free_bird73 gave a link to.

"Actually Ray , to be a smartarse about it, if you don't think nitrates are a problem, then why bother at all, except for burrowing creatures comfort."

You're right you are :)
I do not think Nitrates are a problem at the levels we normally see. At absurb levels of course they are. I use DSB for creature comfort and becuase my tanks seem to stay cleaner with them and the creatures that live in it. Do I get worried about nitrate levels we normally are told are dangerous ( 5,10,20,40 etc)- no.


"I was wondering if a plenum would affect water flow thro' the sand, and I think it might, but at a fiendishly low level by creating more of a 'nitrate gradient' (as it'll increase the nitrate free area and thus push diffusion)"

I do not know; My guess is it would by by a very little amount.

Ray