deep sand beds

[mr.gaboozlebag]

I have looked at many resources, but haven't found how and why a DSB actually works. Most web sites just promote the benefits, not explain the science. So, I'll give you the question, How does a DSB work?

[Reef55]

A DSB works by providing an anaerobic area with a high surface area for anaerobic bacteria to flourish.

The bacteria that break down nitrates into nitrogen are anaerobic (meaning, they do not exist in areas where oxygen is present). So, an effective method to remove nitrates through a biological process means there must be a place for anaerobic bacteria to grow... which is exactly what a DSB provides.


IME, I used to run a 75 gallon tank with an 8" deep sandbed connected to my 120 gallon display. Never had a spec of algae in my display, never detected nitrates. Then I removed all my filtration from my basement to under the tank, and didn't have enough room for the old dsb, so I did not have one anymore. Fast forward 2 months... algae all over the display. I bought a small plastic trashcan that barely fits under my stand, and filled it with 12 inches of sand. I T'd off a section of my return plumbing to feed the container, and had the water just empty back into the sump again. Fast forward another 2 months... algae in the display is gone again.

[mr.gaboozlebag]

Thanks for responding. More Q's:

What animals (if any), do you put in your (trashcan or whatever) to move around the sand, and what kind of sand is it?

[jimmyj7090]

There are a multitude of minute organisms that will inhabit a healthy sand bed. Generally you just seed with LS from the ocean or another established DSB. You want to avoid "sand sifting stars" because they are known to eat all the good stuff and are said to "decimate" the benificial goodies.

Different sources will give different advice on sand type/size. There is no one answer here, but there is much debate. Personally I prefer very fine sand (good old southdown which you cann't buy anymore). I've had good exp with fine, and I'm inclined to beleive that finer sand keeps less crud from settling into the DSB. (Again, there are different opinoins out there....)

One important thing to be aware of, if you do run a DSB in your display it becomes all the more important to have some sort of back up circulation in place in case of a power outage. The bacteria in the sand consume lots of o2 and even more if it starts dying because of no flow. (Pen-Plax B11 pumps, best $15 you'll ever spend before the lights go out)

Oh, and BTW,
Just in case you haven't bumped into this yet, there is/was great debate about the idea that DSB's crash with time. Some reefers did/do feel that DSB is a terrible methodology to use (I'm not one of them at all :) ). Just be aware that there are a LOT of opinions on this topic, so use caution before listening to mine or any other's opinion

[stevenp]

What animals (if any), do you put in your (trashcan or whatever) to move around the sand, and what kind of sand is it?

Bristle worms and pods help move the sand around, and best of all they're free! Nassarius snails do a great job as well.

[randoma]

There's an excellent thread on Remote DSB's on Reef Central, started by Anthony Calfo. Last time I looked at it (several months ago) it had ~60 pages of posts, so it is a long read. :eek:

However, in short, for a RDSB, you want 8-12", or more, of sand, exact kind is not really important although finer is better than courser (although there are a LOT of opinions on this) as courser sand will trap more detritus and will have higher oxygen levels at the bottom. You want reasonably high water flow over the top of the sand, to keep detritus to a minimum. Don't intentionally introduce any 'sand stirrers' (starfish, snails..et al). The idea is to have very little oxygen introduced into the sand bed - sand stirrers will, by virtue of turning the sand over, introduce oxygen into the bed, although if the bed is deep enough, this won't make a whole lot of difference.

Keep in mind that anaerobic, nitrate eating bacteria grow really slowly, so it may take weeks, or months before a new RDSB actually has any visible effect.

That said, on one of my seahorse grow out tanks, which is a 60 gallon tank with a 25 gallon trash barrel sump, with 100lbs of Home Depot play sand (~14" deep), after 2 months, if I do a ~3 gallon water change daily (which I do by virtue of cleaning the tank bottom), nitrates run about 10ppm.

I don't have a 'control' to compare to, so it is possible that the same tank, without the RDSB but still getting the ~3 gallon water change (~25% weekly) would also run very low nitrates... However, this tank gets fed a LOT - 3x/day and has about 100 juvenile/sub-adult seahorses in it, not to mention a handful of other fish/inverts..

I also ran a ~15 gallon sump with 50lbs of HD play sand on our 55 gallon that started leaking. That tank was fairly lightly stocked (2 seahorses, two mandarins, 2 clownfish and a lawnmower blenny) but had <10ppm nitrates with ~25% water changes on a monthly basis. (Nitrates were usually 0, except for 1 month where there was a spike to 40 - I think something died in the tank, but I don't know what as all the fish were accounted for..)

Another advantage of a RDSB is, if you are concerned about the sand bed crashing, it is very easy to change it out...

[mr.gaboozlebag]

Do you know where the thread is, I tried a search, but the server was overloaded. Also, for my sump (a ten gallon aquarium), 8 " seems like a lot, Could I make a DSB sallower?

[randoma]

I wouldn't go less than 6" although 4" might be enough. What you could do is get a tall, narrow container that is sealable - plumb it in-line so the water from the overflow feed into that, then into the sump.

I don't know if this is the original thread I was thinking of, but it is the first one that seems similar that comes up with google. (Google is your friend, use it often!)

Deep Sand Bed In A Bucket (http://www.reefcentral.com/forums/showthread.php?s=&threadid=595109)

[mr.gaboozlebag]

If I put 10'' of sand in 1/3 of my 10g sump, would it be enough for a 40g tank?

[mr.gaboozlebag]

I'm on page 10 of the reefcentral thread, but still don't understand how all the water can be affected by the deep sand bed if the water flows on top of it, not through it.

[randoma]

If you light a stick of incense and put it in the corner of your room, what happens in the rest of the room? Now, if you stick a fan in the window across from the incense, what happens?

Things like nitrates, ammonia, calcium, etc; dissolved solids will diffuse throughout your water column. So, theoretically, at some level you would be able to measure a difference in nitrates at the bottom of the RDSB, but in practice there's no real difference, AS LONG AS there is good water flow over the surface of RDSB. Even though the RDSB is in a separate 'tank', it is still part of the overall water volume.

I have no idea if 10" deep, 1/3rd of a 10 gallon tank would be sufficient - it is really dependent on your bioload and overall ecosystem. However, 6" deep over 2/3rd of a 5 gallon tank, with ample macro algae is barely sufficient for a 15 gallon tank with a high bioload.

I do think you'll run into problems with sand moving/sand storms with 10" of depth in a 10 gallon tank. You'd probably do better with 8".

[mr.gaboozlebag]

My 40g has 4 damselfish currently, some snails, and hermits.

[jimmyj7090]

There is no solid rule of thumb on how much DSB to go with what bioload/tank size.

With depth, I wonder if there is a point of "too much"? IIRC the denitrification actually occurs in the "low o2" condition but if you get to "no 02" there could be a problem. (In other words is there a point/depth where diffusion starts to get limited?)

For the "Remote DSB" thread(s), try looking in the marine depot forums.

Edit, here's a link
http://forum.marinedepot.com/Topic20039-13-1.aspx

[reefkeeper2]

I have a RDSB in a Brute trash can. My tank is over 400gal so I needed a large one. I have a tank with plenty of fish and coral and I feed heavily. My nitrates are very low, so I have to say I think it works great. The only modification I made was to insulate it. I noticed that the plastic was warm to the touch near the top (where the water flows) but cold near the bottom. Since temperature will influence bacterial growth, I thought it would help to keep the little guys warm. Now the entire container is warm top to bottom. Anyway, it has been a success with my setup.

[Greg Hiller]

>I wonder if there is a point of "too much"? IIRC the denitrification actually occurs in the "low o2" condition but if you get to "no 02" there could be a problem.<

I think that you will indeed get to No O2 in a bed without much problem if it's deep enough. I don't think that's a problem. I don't think that having the bed too deep matters much, it just takes up space. While I cannot say I have any numbers, I'd find it difficult to believe that there is enough diffusion going on past about 4 inches in depth that having the bed deeper than that is going to accomplish anything. Maybe if you have it in a glass tank, and can look at the edge of the tank and see critters that are burrowing down below that 4 inches depth, then I'd take my statement back....meaning that if worms or something actively move water and nutrients down deeper into the bed, THEN I might buy that there's some point in having a bed deeper than 4" or so.

[mr.gaboozlebag]

I have a bunch of caribsea Seaflor™ Special Grade Reef Sand. It is 1-2 mm. Would that work for a deep sand bed?



Also, Does the bacteria turn the nitrate into nitrogen gas, or something else, and does the DSB ever get saturated with protein?

[randoma]

You can use the CaribSea, but it would be a waste, in my opinion.. Just get a bag of play sand from HD for $3...

The DSB doesn't get saturated with protein. I have no idea what the waste product from the bacteria is - from everything I've read it isn't an issue.

[jimmyj7090]

The denitrifying bacteria does turn nitrate into notrogen gas.

The idea of the sand bed becomeing saturated with protien (or misc detritis, or other bad stuff) is a big part of the debate on weather DSB is a good or bad methodology. The Anti DSB people will tell you it's almost inevitable. The pro DSB will tell you they've never seen it or see it rarely. It's all about who you listen to since there is no real established set of facts here, just lots and lots of speculation and anecdotal experiences.

I'd think that sand should be fine for a DSB

[6stang9]

I have a 7yr old DSB and have no ill effects, so far. Just remember if you want to end up with a 4" DSB make sure you put 6" of sand to start as it will settle to about 4"