Deep Sand Bed

[jprince]

I have enough sand to cover my 200 to a depth of approx. 3.5 inches. In terms of Nitrate removal, is this considered a DSB? I want to have that much for future stocking needs (Wrasses etc) but I want to avoid the possible "Nitrate factory" issues that some report over long term use. I could move a good amount into the sump if needed prior to setup.

 

[JohnK]

IME on thing a DSB will not become is a nitrate factory. They can get saturated with misc crap and become a phosphate sponge which will eventually start to seep nutrients back into the water. IMO deeper won't make this any worse.

They key to keeping a sand bed long term is most likely to siphion it out partially every couple of yrs.

The deeper you go, the more denitrification you'll likely get (to a point) so nitrate is probably not the thing to be concerned about.

3.5" would be a DSB. Traditionally the reccomendation was always to have 3" or more to create the anoxic conditions needed to support de-nitrifiying bacteria. More reccently there was some testing done (presented @ MACNA 04, anybody have the link?) where shallower sand beds appeared to perform just as well (though I personally second guess some of the interpetation of the results from that testing, but that's a whole nother story).

 

[jrmx635]

dsp

they definately work removing nitraes and are great for critters ,
however If it is stagnant for a long time and you move some rockwork around or desturb it,You can wipe out your tank.
Some people don't realize that and do it accidently.
I have been doing this for 13 yearsish and my current tank has only 1-2 inches.
I also keep horseshoe crabs,sand sifting snails,and sand sifting stars to keep it stirred up.
IMO If you have enough rock,good skimmer and a refugium,you won't have nitrate problems

 

[Jocko]

they definately work removing nitraes...

See this is the thing. What is that statement based on? I believe the study that jimmyj is referring to was the one done by Rob Toonen. He presented it at one of the BRS meetings a few years back. The results were that choice of bottom substrate thickness (including bare bottom) made no noticeable difference on water quality.

Which doesn't necessarily mean that a DSB doesn't have the potential to process more nitrate, but I think it means that the system as a whole has so much processing capacity as it is, that a DSB never really has the chance to be utilized in that manner. But then again, I'm not aware of any specific study that shows that the DSB does in fact turn into a nitrate reduction machine. I think it's more just an assumption. I'm not 100% sure though.

So the short of it is, choose whatever works for you aesthetically and for the requirements of the livestock you want to keep. The rest of your system's design will impact your water quality WAY more than your choice of sand bed.

 

[MikeG]

I believe there have also been studies done about DSB depth using the remote bucket method and determining the reduction in nitrate in the water column in relation to the sand bed depth. I could be remembering that wrong but the general idea from what I remember was that there was a depth that gave the best effeciency and I believe it was around 6" and there was also a depth where there was no more additional benefit and I believe that was around 12". Not sure how this would differ from a DSB in a tank. Think it was a couple years ago on RC when remote DSB were just coming into fashion.

 

[Jocko]

Yeah I think part of the problem is that along the way, anecdotal evidence gets passed around and people start to believe it's gospel. It's really the same thing that led to the sandbed wars in the past. Some person would say "I switched to a deep sand bed on my new tank and now I don't have nitrates." And they leave out all of the other variables in the equation like they got a new skimmer or they changed what the feed, etc.

I believe that Rob said that was one of the motivators behind doing his experiment. He could control the variables and give some usable and reliable results. It's hard to tell from random people's forum posts if they actually took any sort of semi-scientific approach to determining the effectiveness of what they are doing.

Although the nice thing with the remote DSB is you can always just add one later if you do find that you have nitrate problems. So it's nice having it as an option.