Deep Sand Bed

[flavescens]

This is sort of a two-fold question:

First, what is the benefit of a deep sand bed? It would seem to me that a layer of sand is fine no matter what depth because only the surface comes in contact with the water anyway.

Second, what actual depth constitutes a "deep" sand bed?

 

[scavdog]

One of the principal benefits to deep sand bed methodologies is the potential for natural nitrate reduction (NNR). The speed and extent to which a DSB can reduce nitrate in an aquarium amazes many aquarists? especially those that have struggled with nitrate control for any length of time through other means. The benefits to an established tank with the upgrade to a DSB are apparent in just a few weeks with potential for complete nitrate reduction (to ?zero?)!

Read more here

http://www.wetwebmedia.com/deepsandbeds.htm

 

[ScooterNH]

That's an excellent article. Thanks for posting it.

I'd like to add a few comments on things that I've done with my DSB. I had researched a lot before setting mine up. Hope it helps.

- I incorporated a plenum (and as the article states, this is totally optional. It 'made sense' for me so I did it.)

- My DSB basically has two main layers separated by screening.

The lowest 3" is non-aragonite course sand (this may or may not be correct practice, but I didn't want it dissolving over time). Regardless of the sand grade, what's important is that I covered this layer with plastic screening. This is to keep burrowers (snails, crabs, engineer gobies, jawfish etc) from disrupting the lowest parts of the sand bed. On top of that I have 3-5" (it varies - see gobies below) of fine/medium grade aragonite sand.

Before adding the 2nd layer, I placed a number of "pedestal" rocks. These were roughly about fist sized with flat bottoms and tops. They sit on top the screen, and serve two purposes: First to support the upper layers of liverock from shifting and also to keeping the bulk of my liverock up "off" the sand bed for better flow. Once the pedestals were where I wanted them, I added the top layer of sand around these bases.

(I made my support pedestals of aragrocrete (cement/shell mix), but 3" pvc pipe would work well too).

I'm very glad I took the time to do the screen layer and the pedestals, because I have two engineer gobies that are CONSTANTLY TUNNELING everywhere. And in the couple places where I have chunks of live rock just sitting on top the sand (not on the pedestals), these are always shifting/sinking due to the various excavators in my tank.

 

[Matt L.]

Scoot,

The screening idea is brilliant. Was that your novel idea? If so, you deserve a reef award for ingenuity.

Personally, I don't use a DSB (just a sand bed). I just thought it was a really neat idea.

Matt

 

[ScooterNH]

The screening idea is brilliant. Was that your novel idea? Matt

Unfortunately, no, I had read it somewhere first. Not even sure who to give credit to. ;-( But someone out there deserves praise. it works very nicely in my larger tank.

I also learned the hard way on my first smaller tank. That also has a DSB, but I didn't do the screen or pedestal tricks (I learned about months later). For that tank I made my own aragrocrete rock formations. These were basically shelf pieces and small arches that had 2-3" pillar feet. I wanted to keep things off the sand bed. These have completely sunk into the sand and every now and then I try to pull them back up. But that's always turned out to be difficult and disruptive.

 

[JohnK]

Just to add, there is/was a debate raging about DSB is "good" vs DSB is "bad".

The good has already been touched on, the bad was the notion that at least in some cases the DSB can end up acting like a sponge for detritis and whatever other bad stuff over time, eventually becoming "saturated" and either leeching out "bad stuff" or otherwise causing problems and or "old tank syndrome".

Personally I'm in the DSB is "good" camp, but I thought it might be helpful to mention the flip side of the coin.

Also there is an article in this months advanced aquarist that touches on some of this, I just skimmed it so I'm fuzzy on the details, but It might be worth checking out.

If no one mentioned it yet, IIRC the consensus is generally that for a DSB to be effective as a DSB (good denitrification) it should be a min of 3" deep, with 4" or more being better.

Personally I've kept a DSB for several years with no problems, and never a detectable nitrate reading.