What makes a deep sand bed?

Cobystolz · May 22, 2019

Is this considered a deep sand bed? It’s 2.5 inches deep. I’m redoing my sand and don’t want to deal with the problems of them like not being able to strut it.

sghera64 · May 22, 2019

I believe common consensus holds that a true DSB is >4-inches deep on average across the bottom.

Beds that are 2-4 inches deep are hybrid and less than 2 inches are considered a shallow sand bed.

There is no quantifiable measure of what is really a DSB and no established standards of the the minimally achievable levels of desired effects (denitrification capacity and other processes). These all depend on more than depth. They depend on what is in the water, on the sand, in the sand, the type and size of sand, sand sifting/ turning, bulk water motion and more. Further complicating the matter is hybrid systems with plenums beneath the sand (Dr. Jubert) or reverse flow under gravel filter (Paul B.).

If you add sand, you are increasing surface area for certain. At some point, and in a number of small locations in even a shallow sand bed, you will begin to have “dead spots” where anaerobic activities occur and exhibit DSB characteristics (both the good and bad ones).

Perhaps others can chime in and share more.

FYI, I’ve had a DSB in my 135 gal DT for 17 straight years with no problems, no sand change-outs. I do sift by hand occasionally and have to add more sand as it does “disappear” somewhere over time.

jda · May 22, 2019

I consider a DSB when it is able to crush nitrate to where there are barely any. This happens for me at about 3". I won't do 4-6 inches anymore, but those used to be really common... I just don't see the reason to tie up the extra three inches of tank space.

Grain size of the media will make a huge difference. Larger media will need a deeper bed.

Edit: I do like to siphon mine starting in about year four. I do 1/4 of the exposed sand every 3 months. Even though detritus is benign, I do find that it can "gum up the works" where even the cucumbers and conchs wander more. All of the sand dwelling creatures tend to prefer the cleaned areas over the dirty ones. I duplicate this after the next 3 or 4 years.

You can also lose sand as it dissolves with the lower pH down near the bottom. This is normal, but you might have to add more if your tank is prone to lower pH anyway. I might add 40 pounds ever 4-5 years.

Cobystolz · May 22, 2019

sghera64 said:
I believe common consensus holds that a true DSB is >4-inches deep on average across the bottom.

Beds that are 2-4 inches deep are hybrid and less than 2 inches are considered a shallow sand bed.

There is no quantifiable measure of what is really a DSB and no established standards of the the minimally achievable levels of desired effects (denitrification capacity and other processes). These all depend on more than depth. They depend on what is in the water, on the sand, in the sand, the type and size of sand, sand sifting/ turning, bulk water motion and more. Further complicating the matter is hybrid systems with plenums beneath the sand (Dr. Jubert) or reverse flow under gravel filter (Paul B.).

If you add sand, you are increasing surface area for certain. At some point, and in a number of small locations in even a shallow sand bed, you will begin to have “dead spots” where anaerobic activities occur and exhibit DSB characteristics (both the good and bad ones).

Perhaps others can chime in and share more.

FYI, I’ve had a DSB in my 135 gal DT for 17 straight years with no problems, no sand change-outs. I do sift by hand occasionally and have to add more sand as it does “disappear” somewhere over time.

Than you, that makes me feel better about it now. I was just worried I was gonna mess something up. Hopefully everything will end up being fine.

Cobystolz · May 22, 2019

jda said:
I consider a DSB when it is able to crush nitrate to where there are barely any. This happens for me at about 3". I won't do 4-6 inches anymore, but those used to be really common... I just don't see the reason to tie up the extra three inches of tank space.

Grain size of the media will make a huge difference. Larger media will need a deeper bed.

Edit: I do like to siphon mine starting in about year four. I do 1/4 of the exposed sand every 3 months. Even though detritus is benign, I do find that it can "gum up the works" where even the cucumbers and conchs wander more. All of the sand dwelling creatures tend to prefer the cleaned areas over the dirty ones. I duplicate this after the next 3 or 4 years.

You can also lose sand as it dissolves with the lower pH down near the bottom. This is normal, but you might have to add more if your tank is prone to lower pH anyway. I might add 40 pounds ever 4-5 years.

Ok thanks, I already have low nitrates and almost need more because my corals seem to like it a little dirtier, at least my gsp and Xenia. My birdsnest also seemed to grow a little faster with more nutrients. With the large grains at only two and a half inches do you think it will dissolve? If it will does it add calcium?