Deep Substrate Bed - Denitrification
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Old 02-13-2013, 04:01 AM   #1
RobMc
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Deep Substrate Bed - Denitrification


I've recently been spending a lot of time researching saltwater reef systems. In a reef tank it is general practice to have a sump with a refugium. Often times the main display tank or the refugium will have a deep sand bed of 4+ inches for the purposes of denitrification.

If one were to establish a deep substrate bed in a freshwater tank, would the same or similar anerobic bacteria form?

Do the lower oxygen levels have a negative effect on the roots? Or will the roots just not grow at this level anyway?

Would a system like this benefit from a black worm or snail population to turn the substrate?

I would like to take this approach with my next tank.
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Old 02-13-2013, 04:14 AM   #2
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I am curious about this, too. Lotta people here talk about anaerobic areas being bad in freshwater aquaria, but the whole idea of a deep sand bed in marine applications is that there are denitrifying bacteria that grow under anaerobic conditions.
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Old 02-13-2013, 04:19 AM   #3
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Interesting article:

http://www.wetwebmedia.com/ca/volume...e_7_1/dsb.html
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Old 02-13-2013, 03:14 PM   #4
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Quote:
Originally Posted by RobMc View Post
I've recently been spending a lot of time researching saltwater reef systems. In a reef tank it is general practice to have a sump with a refugium. Often times the main display tank or the refugium will have a deep sand bed of 4+ inches for the purposes of denitrification.

If one were to establish a deep substrate bed in a freshwater tank, would the same or similar anerobic bacteria form?

Do the lower oxygen levels have a negative effect on the roots? Or will the roots just not grow at this level anyway?

Would a system like this benefit from a black worm or snail population to turn the substrate?

I would like to take this approach with my next tank.
It was established decades ago via a process known as guttation vascular aquatic plants create a very slow flow within the substrate. It's also know for an equally long time vascular aquatic plants transport oxygen down into the substrate via the roots.

Snails and black worms may work, but I'd be concerned that a population of black worms without predators too keep the population in check might end up in a wormy mess.

Last edited by Steve001; 02-13-2013 at 03:24 PM.. Reason: x
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Old 02-13-2013, 03:47 PM   #5
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Very good article sluggo, that's the kind of information I was looking for.

So, Steve - the ebb and flow of pressure in the plants' roots is enough to slowly turn the substrate? I would still think that worms / snails would help bring more nutrients / oxygen to the depleted areas around the roots regardless of the guttation or O2 transport.

More supplemental O2 to roots = Better?
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Old 02-13-2013, 04:04 PM   #6
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So here is what I was thinking.

Sump with refugium - no filter floss / fine media prior to the fuge section
4-5 inches of fine grain sand (in fuge)
Flow across the top of the water column only - allowing detritus to settle

Flora:
floating plants to remove excess nutrient from water column
Java moss to supply supplemental diet for the fauna
eventually crypts to lower base nutrients in the substrate

Fauna:
Red cherry shrimp or pond snails to eat the dying floaters / java
black worms or tubifex for substrate aeration / breakdown of settling organics.

In this experiment I would like to have a dominant population of red cherry shrimp as I've read that older RCS will eat black worms - however blackworms will most likely out-reproduce RCS if given the chance. It will take a while before detritus starts seeping into the lower levels of sand, so I think a few months with just RCS would do it. Tubifex worms may be a better option as they will stay out of the water column and may burrow deeper into the substrate.
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Old 02-13-2013, 04:16 PM   #7
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Speaking of saltwater practices translating to freshwater, I wonder if anybody out there runs a freshwater algae scrubber?
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Old 02-13-2013, 04:23 PM   #8
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Default Re: Deep Substrate Bed - Denitrification

No algae scrubber, but I have a tank with a deep sand bed... Like six or more inches deep. I have no idea if it is making a difference or not.

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Old 02-13-2013, 04:27 PM   #9
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In the saltwater aquarium you don't have plant roots. Denitrification occurs in the live rock and the sand bed if it's not stirred and deep enough to have anaerobic areas. Some of the bacteria in the biofilm are optional denitrifiers in the absence of oxygen.

This also applies to freshwater aquariums. What happens is the plants can alter the substrate to extract nutrients from it with their roots.

As long as the substrate has nutrients in it, it will help plants and roots will grow. If the sand is inert and has a low granularity it will promote growth of anaerobic microorganisms and reactions resulting in all kinds of nasties to form in there. Gases like methane and hydrogen sulfide which are highly toxic will result from these anaerobic reactions.
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Old 02-13-2013, 08:24 PM   #10
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Quote:
Originally Posted by RobMc View Post
Very good article sluggo, that's the kind of information I was looking for.

So, Steve - the ebb and flow of pressure in the plants' roots is enough to slowly turn the substrate? I would still think that worms / snails would help bring more nutrients / oxygen to the depleted areas around the roots regardless of the guttation or O2 transport.

More supplemental O2 to roots = Better?
Guttation allows new water from the main body of the tank that has oxygen to replace water lower in oxygen in addition to what the roots deliver. Though it doesn't turn over the substrate like critters would. I've only seen snails [ I have Malaysian live bearing snails] move substrate and as for worms it would be difficult to see how such a week critter could move a pebble or some other type of not dirt substrate. Has it been clearly demonstrated worms and snails actually turn over a substrate [ like ants or earthworms] or do they in the case of snails just move the very top layer around ?
Snails and worms along with a plethora of other substrate critters work well in a natural environment, but maybe not so well in a closed system. The important thing is to have a very slow flow of new water from the main body of the tank through a substrate that does not compact.
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Old 02-13-2013, 08:27 PM   #11
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Quote:
Originally Posted by RobMc View Post
So here is what I was thinking.

Sump with refugium - no filter floss / fine media prior to the fuge section
4-5 inches of fine grain sand (in fuge)
Flow across the top of the water column only - allowing detritus to settle

Flora:
floating plants to remove excess nutrient from water column
Java moss to supply supplemental diet for the fauna
eventually crypts to lower base nutrients in the substrate

Fauna:
Red cherry shrimp or pond snails to eat the dying floaters / java
black worms or tubifex for substrate aeration / breakdown of settling organics.

In this experiment I would like to have a dominant population of red cherry shrimp as I've read that older RCS will eat black worms - however blackworms will most likely out-reproduce RCS if given the chance. It will take a while before detritus starts seeping into the lower levels of sand, so I think a few months with just RCS would do it. Tubifex worms may be a better option as they will stay out of the water column and may burrow deeper into the substrate.
Before you go whole hog you might want to do a proof of concept with a small tank.
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Old 02-13-2013, 09:45 PM   #12
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does anyone use those buried heat cables anymore? I thought one of the benefits of those was supposed to driving a very slow flow of water through the substrate.
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Old 02-14-2013, 01:11 AM   #13
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Quote:
Originally Posted by Sluggo View Post
Speaking of saltwater practices translating to freshwater, I wonder if anybody out there runs a freshwater algae scrubber?

There is a fairly long thread on this. It involves a separate tank with high light output shining onto water outflow panel, and involves weekly "scrubbing" of algea off panel.
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Old 02-14-2013, 09:52 AM   #14
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Quote:
Originally Posted by danielt View Post
In the saltwater aquarium you don't have plant roots. Denitrification occurs in the live rock and the sand bed if it's not stirred and deep enough to have anaerobic areas. Some of the bacteria in the biofilm are optional denitrifiers in the absence of oxygen.

This also applies to freshwater aquariums. What happens is the plants can alter the substrate to extract nutrients from it with their roots.

As long as the substrate has nutrients in it, it will help plants and roots will grow. If the sand is inert and has a low granularity it will promote growth of anaerobic microorganisms and reactions resulting in all kinds of nasties to form in there. Gases like methane and hydrogen sulfide which are highly toxic will result from these anaerobic reactions.
Hydrogen sulfide will probably form. If not released, life will likely form to break it down. Pockets like this form in sw beds when disturbed but are shown to vanish with time. The goal is to only disturb very small sections at a time (snails and worms) .

A fine sand will be used. Maybe even mineralized dirt without a cap. Since the flow will be minimal and there won't be any large fauna to stir up the bed it may work. Such a bed would be better suited for microorganisms and would also release micronutrients into the wc.

Edit - water column alkilinity may be an issue

Last edited by RobMc; 02-14-2013 at 10:20 AM.. Reason: edit
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Old 02-14-2013, 10:02 AM   #15
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Before you go whole hog you might want to do a proof of concept with a small tank.

Agreed, I'll keep it to a sump for sure - this way it can be detached from the system if anything goes wrong.

I have been using a sump + fuge on this tank here
http://www.plantedtank.net/forums/sh...545&highlight=
And it has been working quite well. I've been using floaters for nutrient export but the dsb sounds like a more comprehensive approach.

Last edited by RobMc; 02-14-2013 at 10:16 AM.. Reason: info
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