Sand bed depth...

[saltywhit67]

Since i have been looking in to setting up my new aquarium i have received much advice on the depth of the sand bed topic. I have heard 150 lbs, i have heard 4 - 6 inches. Today i picked up my saltwater aquarium handbook and discovered this: "The amount of material for an aquarium is mainly dependent on whether you are using an undergravel filter. With an undergravel filter a recommended depth of bottom material is 2.5 to 3.0 inches" It then goes on to say it can be even deeper than that with the undergravel. "In aquariums without an undergravel filter, a shallow layer of substrate is all that should be used to cover the bottom, with a depth of not more than 1/2 to 3/4 of an inch of substrate" why? "The bottom depth must be restricted to minimize the possibility of anaerobic bacterial activity. These bacteria develop in filter beds where there is restricted water flow to carry dissolved oxygen. Without a constant water flow through a filter bed, the substrate favors the growth of anaerobic bacteria, producing toxic gases such as methane and hydrogen sulfide".

 

[bang guy]

I think you need a better book
Sandbeds are optional. There are a wide variety of ways to filter an aquarium and Sandbeds are only one way. If you just want biologic filtration then 1/2" of sand is fine. If you want to remove Nitrate then you will need at least 3" of very fine sand and a plethora of infauna. If you want to remove Sulfur then you'll need at least 8".

 

[astroclown]

I won't go thinner than 3" of sand for my 70gal, but it all depends on how fine your sand is and tank height. The finer the sand is the better it is, for the bacterila against larger grains. Smaller grains have much larger surface area for bacteria to grow into, than larger ones. So if you have wider but shorter you would need less bedding, higher but narrow need deeper bedding. It doest really matter on the depth, what matters more is the type of grain you have.

 

[dreeves]

The methane I do not know...the sulfur is true given certain circumstances...
I could be wrong, but I believe the sulfur will be present dependent upon the amount of nitrate processed...as with too much processing or better, to fast of processing can and usually does create the sulfur...which in most instances is harmful...but, they amount of water flow to the O2 deprived portion of the bed is restricted greatly which in most instances prevent this from happening...There is no open flow of the water column in the sand bed...most depend upon worms and so forth to generate the movement needed to process the water down through the depths...
In the home marine environment...nitrate is tough to remove...one of the possible ways to either remove it, or in the case of a DSB, is to allow the complete nitrogen process to occur...this is the consumption of the nitrate with the release of nitrogen as the result...it is also a semi-heavily discussed topic here and abroad as to which is better...the DSB, water changes, etc....most will use a combination of several methods to aid in the control of the nitrate issue...
Most will also advise the depth of 5-6 inches is ideal for the DSB to work...
Something else to consider (scrap the UGF) is a plenum system...MightyJuiceOx on here I believe is familiar with those...
The book is correct though...