Eheim Subtrate below DSB

[fish_head]

Hi,

I was wondering whether adding a single layer of Eheim Pro Substrate at the base of the DSB would increase the efficiency of the breakdown of nitrates.

Since the substrate has an extremely high surface area to volume ratio, it would be able to house a much larger colony of anaerobic bacteria than just the space between the sand..am i right?

what are your thoughts on this?

thanks

[crazylegs]

http://www.saltcorner.com

Check out this site. There are many articles on substrate and the bacteria within. It says to go for anoxic zones not anaerobic zones. It's a bit technical, but you should be able to get the point.

[fish_head]

i thought the anoxic zones was where the anaerobic bacteria lives?

[ruprecht]

It appears (http://www.seachem.com/support/SpecificSurface.pdf) that Eheim Pro Substrate has a surface area of around 0.2171 m²/g. Does this have more surface area than sand? Depends on what kind of sand you are using. Say 1mm sand grains... (2.65gm/cm³) (10-3m²/cm³) (http://www.owlnet.rice.edu/~chbe402/Hirasaki/CHAP3D.pdf) = 0.004 m²/g. So 0.1mm diameter sand would be 0.04 m²/g.

Take the numbers for what you will, it is the internet after all.

[crazylegs]

The terms anoxic and anaerobic seem to have different meanings to different people. I've seen anoxic used to describe oxygen free and low oxygen zones. anaerobic is generally agreed upon as being oxygen free. I haven't really taken the time to break out the "Webster's" and see what it says.

What it comes down to, is whether or not you belive a DSB works, and for what reason it works. I can provide you with links that show it works due to advection. I can provide you with links that show it works due to infauna. I can provide you with links that say it hinders more than helps.

Assuming a DSB works, based on either advection or infauna, I don't see this material working well in either application. It will not respond to advection as will fine grain sand. It cannot be burrowed thru or turned over by infauna as can fine grain sand.

That's just my guess. If you try it, post it so we can see how it goes.

[fish_head]

what i'm trying to say is not using the substrate to replace the whole sand bed but placing a layer at the base of the sand or having a small amount scattered throughout the sand bed to give more surface area for the bacteria to colonize

i always thought the dsb worked with the aerobic nitrifying bacteria in the upper layers converting ammonia to nitrite to nitrate and thus depleting the water of oxygen as it diffuses down into the deeper layers where anaerobic de-nitrifying converted nitrates into nitrogen gas in the formula:

6 NO3- + 5 CH3OH --> N2 + 5 CO2 + 7 H2O + 6 OH-

[crazylegs]

What you are saying is correct. However the debate around DSB's is the process by which the water is moved within the sandbed and the aerobic & anaerobic bacteria. Some claim that infauna are responsible for turning over the sandbed and causing the proper conditions for denitrification. Others claim that advection and the flow above the substrate causes small pressure differences within the sandbed which are responsible for nutrient transfer. Either way, the nitrates must make their way to the anaerobic bacteria, and the nitrate free water must make it's way out of the sandbed. I'm not saying that these processes do not take place. I'm saying that there are several debates as to how they take place. The two prevailing arguments are infauna and advection. Given those two arguments, I'm doubtful that a large particle substrate will be of benefit.

Maybe with a Jaubert system, where the denitrification process is soley dependant on bacteria and the molecular charge of nutrients, this substrate might be of benefit. There are still too many uncertainties with DSB's to say if this idea will work or not. So, let's look at both arguments and see how this substrate would interact.

If DSB's perform denitrification mainly due to infauna slowly turning the sandbed, it would be dependant on their ability to physically move the substrate. We're talking about micro brittle stars and polycheates. At least, those are some of the larger fauna performing these functions. I seriously doubt their ability to physically move or turn over such large particles. IF they only operate in the upper layers of the sandbed, then your idea might be beneficial. But nobody has absolutely proved how infauna operate in a DSB and to what extent when it comes to denitrification.

If DSB's function by advection and minute pressure differentials caused by variations in the substrate surface, then your idea may hold more validity. However, the amount of flow between a fine grain substrate is greatly reduced within the top inch of sand. When you propose using a larger sized particle, the flow of water between these particles will be greater to a greater depth. Regardless of the amount of bacteria these particles house, you still have to produce a low oxygen environment before denitrification can take place. If you have stronger flow through the top layers of substrate, you will have more oxygen in the top layers of substrate. Thus your bed must be deeper. Since you propose using this material only on the bottom, the chances of low oxygen water making it to your eheim layer are greater. This scenario might actually work, if DSB's operate based on advection.

Either way, I feel that there are too many unknowns. But your idea certainly would test some theories. So, by all means try it. Please, I ask, document it so that we can all see how it goes.

[fish_head]

thanks for the input

I went ahead and did what i suggested and put a layer of the substrate beneath the 5-6" bed. We'll see how effective it is at reducing nitrates once it becomes established;)

[crazylegs]

Out of curiosity, did you seperate the two layers in anyway? Like they say to do with the Jaubert system plenum. It will be interesting to see how this works out for you. Good luck!

[Aquarist007]

What you are saying is correct. However the debate around DSB's is the process by which the water is moved within the sandbed and the aerobic & anaerobic bacteria. Some claim that infauna are responsible for turning over the sandbed and causing the proper conditions for denitrification. Others claim that advection and the flow above the substrate causes small pressure differences within the sandbed which are responsible for nutrient transfer. Either way, the nitrates must make their way to the anaerobic bacteria, and the nitrate free water must make it's way out of the sandbed. I'm not saying that these processes do not take place. I'm saying that there are several debates as to how they take place. The two prevailing arguments are infauna and advection. Given those two arguments, I'm doubtful that a large particle substrate will be of benefit.

Maybe with a Jaubert system, where the denitrification process is soley dependant on bacteria and the molecular charge of nutrients, this substrate might be of benefit. There are still too many uncertainties with DSB's to say if this idea will work or not. So, let's look at both arguments and see how this substrate would interact.

If DSB's perform denitrification mainly due to infauna slowly turning the sandbed, it would be dependant on their ability to physically move the substrate. We're talking about micro brittle stars and polycheates. At least, those are some of the larger fauna performing these functions. I seriously doubt their ability to physically move or turn over such large particles. IF they only operate in the upper layers of the sandbed, then your idea might be beneficial. But nobody has absolutely proved how infauna operate in a DSB and to what extent when it comes to denitrification.

If DSB's function by advection and minute pressure differentials caused by variations in the substrate surface, then your idea may hold more validity. However, the amount of flow between a fine grain substrate is greatly reduced within the top inch of sand. When you propose using a larger sized particle, the flow of water between these particles will be greater to a greater depth. Regardless of the amount of bacteria these particles house, you still have to produce a low oxygen environment before denitrification can take place. If you have stronger flow through the top layers of substrate, you will have more oxygen in the top layers of substrate. Thus your bed must be deeper. Since you propose using this material only on the bottom, the chances of low oxygen water making it to your eheim layer are greater. This scenario might actually work, if DSB's operate based on advection.

Either way, I feel that there are too many unknowns. But your idea certainly would test some theories. So, by all means try it. Please, I ask, document it so that we can all see how it goes.

great summary of the two scenarios or differences in thought. I believe that advection is also just theory like infauna??

[fish_head]

Out of curiosity, did you seperate the two layers in anyway? Like they say to do with the Jaubert system plenum. It will be interesting to see how this works out for you. Good luck!

no i just placed a layer at the bottom of the sump compartment and then dumped the sand on top. i also scattered a few bits throughout the sand.

Even if this does end up being more/less efficient than not having the substrate in at all, i don't have a real method of testing the difference=/

[ibnozn]

tests on different grain sizes with and without plenums if it'll help you:
http://www.advancedaquarist.com/2005/6/aafeature
http://www.advancedaquarist.com/2005/7/aafeature/

crazylegs, I think the denitrification process in a sand bed is dependent on both the infauna and bacteria, not solely one or the other. The infauna are responsible for breakdown and processing of organic wastes and sand turnover in the upper layers of the sand bed and it's this process that enables advection of water into the lower layers of the bed where anaerobic denitrifying bacteria reside. Water could not circulate properly through the bed without the infauna present to process the constant influx of settled organic material. The bed would become "clogged" and denitrifying bacteria populations would suffer from lack of circulation. Infauna are a form of "mechanical" filtration while bacteria residing in the lower layers of the bed provide a biological and chemical filtration function.