Deep Sand Beds: How does it work?

[wscttwolfe]

So from what I've been reading, a deep sand bed is essentially a place where there is very very little water flow, which means oxygen levels will be low. This creates an environment which is perfect for anaerobic bacteria to grow in. These bacteria then consume nitrates in the tank water. If this is correct than I have two questions:

(1) If there is very very little water flow, how does the nitrate-loaded tank water get into the DSB at a rate high enough to have any meaningful impact on nitrate levels?

(2) If the anaerobic bacteria are consuming nitrate, what are the waste products of this nitrate consumption?

I'm asking because I just did a sloping DSB in my RSM 130D tank, starting with 3" in the front, and gradually going up to 5 1/2" - 6" in the back

 

[steved13]

There is some flow, and I believe there is a "sweet spot" (low enough flow, yet enough turn over) in the layers where it takes place.

It's converted to nitrogen gas.

 

[msalih81]

I'm so confused now, I thought "dead spots" are bad? I was watching this guy on youtube aquascaping and he said when you build the rocks to leave as much openings as possible because it'll grow anaerobic bacteria?

 

[PSU4ME]

in the tank dead spots are no good......down under the sand bed, they do good things.

 

[steved13]

I'm so confused now, I thought "dead spots" are bad? I was watching this guy on youtube aquascaping and he said when you build the rocks to leave as much openings as possible because it'll grow anaerobic bacteria?

Probably the easiest way to think about it might be...dead spots that you can avoid should be avoided, IE: on the sand bed, between or around rocks, keep it moving. Anaerobic bacteria grow in "dead spots" that can't be avoided IE: deep inside the rock, or deep in the sand. In a deep sand bed you could move it around and eliminate the dead spots that way, however then you might as well have a shallow sand bed. In a shallow sand bed you won't get any anaerobic bacteria and it should be kept stirred, to eliminate other nasties.

So the advice is good because he's telling you to eliminate dead spots that you can eliminate, and the other "dead spots" you can't eliminate no matter what you do.

 

[sasquatch]

imagine a 5 gallon pail of sand, at the bottom of the bucket is a cup of gasoline, fill bucket with water... will you smell gasoline? the water flow across the sand act like the lift under an airplane wing, it draws the lower (in sand) water up creating very slow flow while new water is drawn into the vacant space

(1) If there is very very little water flow, how does the nitrate-loaded tank water get into the DSB at a rate high enough to have any meaningful impact on nitrate levels?

I'm so confused now, I thought "dead spots" are bad? I was watching this guy on youtube aquascaping and he said when you build the rocks to leave as much openings as possible because it'll grow anaerobic bacteria?

There has been a lot of fear about H2S (hydrogen sulfide) building up under rockwork, giant gas bubbles wiping out tanks blah blah blah, those "deadspots" have more activity going on than anywhere else, its a natural compost heap, the gas that comes out is very minor, stirring up a pocket would have very bad effects but so does poking a bee hive so like Mommy says "don't pick at it or it will bleed"

 

[msalih81]

ah I see, thx =)

 

[tekjunkie28]

imagine a 5 gallon pail of sand, at the bottom of the bucket is a cup of gasoline, fill bucket with water... will you smell gasoline? the water flow across the sand act like the lift under an airplane wing, it draws the lower (in sand) water up creating very slow flow while new water is drawn into the vacant space

(1) If there is very very little water flow, how does the nitrate-loaded tank water get into the DSB at a rate high enough to have any meaningful impact on nitrate levels?




There has been a lot of fear about H2S (hydrogen sulfide) building up under rockwork, giant gas bubbles wiping out tanks blah blah blah, those "deadspots" have more activity going on than anywhere else, its a natural compost heap, the gas that comes out is very minor, stirring up a pocket would have very bad effects but so does poking a bee hive so like Mommy says "don't pick at it or it will bleed"

Right sad but how does a hydrogen sulfide bubble form that would be big enough to take out a tank?? How d would the bubble just rise to the surface and pop? Who does that wipe out a tank?

PS I have bubble form in my rather deep sand bed in a cichlid tank... Lots of small bubbles. Same thing?

 

[wscttwolfe]

from what I understand the bubble could very well just be nitrogen gas, a byproduct of nitrate breakdown

 

[ddelozier]

H2S gas AKA Hydrogen Sulfide isnt good for your tank, it can absorb oxygen, becoming H2SO4...aka Sulfuric acid, which can do very very nasty things to your PH. You have probably heard it said that PH in a closed system(aka Aquarium) naturally tends to drop. This is why. the "Dreaded Dead Spots" Create alot of H2S, if it cant be released IE sand sturing critters, It will over time turn into H2S04 and drag down the PH...if your ph drops too far or too fast, your tank will crash. I havent seen it first hand, but i have known people who were victims of this.

 

[zchauvin]

(2) If the anaerobic bacteria are consuming nitrate, what are the waste products of this nitrate consumption?

This^ Why I don't really want to put a dsb in my tank but will try, the same as chaeto... I don't know about either. DSB may take it out of the water but it won't take it out of your tank same as chaeto, you have to manually remove it. Everything in a DSB has to produce waste. Some people like it, I don't favor it honestly. A protein skimmer is the only thing that actually removes organics from your water before they turn into nitrates. Then you just dump it out, still its completely out of the system. Just my .02

 

[lbiminiblue]

Nitrogen gas is the product of nitrate consumption. Beats me how the gas gets out of the DSB. LOL don't sweat the stuff you don't understand, nature does its thing...lol.

 

[lbiminiblue]

Well the bubble could rise and pop if a sand sifting star stirred up enough sand and the bubbles somehow got up...or maybe a bristle worm or peanut worm digs a tunnel that acts as a canal for the bubble...it happened to me a few times when i was trying to catch my dragon wrasse- i stuck my hand in the sand and when he popped out, along with bubbles, i netted him. But nothing happened to my tank. I don't understand how the bubble would "kill"the tank if all it does is rise and pop and let all the hydrogen sulfide into the air...

 

[Dracko]

I have heard of lakes doing this too. They call it "turning over" when a gas pocket gets so big that it literally turns over a large area of the bed and causes massive die off of the fish. But in a lake, you have a mud bottom. You also have a large volume of that soil holding in a lot of gas. In a tank you have sand and a smaller volume. It's hard for me to imagine any bubble getting large enough to do real damage. I'm no expert, but I've never had it happen in any of my mud bottom freshwater tanks.

 

[sirrealism]

This^ Why I don't really want to put a dsb in my tank but will try, the same as chaeto... I don't know about either. DSB may take it out of the water but it won't take it out of your tank same as chaeto, you have to manually remove it. Everything in a DSB has to produce waste. Some people like it, I don't favor it honestly. A protein skimmer is the only thing that actually removes organics from your water before they turn into nitrates. Then you just dump it out, still its completely out of the system. Just my .02

Agreed accept for the fact that you will have inorganics in your tank. The skimmer cant take out everything, so then what? you need the bacteria that is in your rock, DSB, chaeto and my new favorite algae scrubbers. It does not matter how good your skimmer is it cant remove inorganics When we test N03 and P04 we are not testing for organics but inorganics. No doubt a good skimmer helps to keep A tank clean of organics but you cant get away with just organic removal. This is why we need rock or something to let the bacteria grow in it so the bacteria can use up the inorganics.