# Freshwater Deep Sand Bed Idea for Low Tech Setup



## solarz (Aug 31, 2010)

One of the limiting factors for low tech setups is CO2. With smaller tanks I've used DIY, but I frequently neglected to change bottles regularly, and over time even that became a chore. With larger tanks, DIY isn't even a viable option.

CO2 is a natural byproduct of respiration, and every living organism in an aquarium produces CO2. Theoretically, we should be able to increase the dissolved concentration of CO2 in the water column by having a bigger bioload.

Unfortunately, fishes produces a lot more ammonia than CO2, and this could lead to water quality issues, so adding more fishes isn't the answer. However, fishes are not the only organisms that produce CO2 in the aquarium. Bacteria, more specifically nitrifying bacteria, also produce a lot of CO2.

Nitrifying bacteria need surface areas to live. The more surface area, the bigger its population. To provide this surface area, we usually use filter media. However, there is another source of surface area, and that is the substrate.

In SW, people often use deep sand beds to cultivate anaerobic *de*nitrifying bacteria that turns nitrates into harmless nitrogen gas. These anaerobic bacteria live in the deepest, anoxic parts of the sand bed. The shallower parts of the sand bed are populated by the aerobic nitrifying bacteria.

In freshwater context, this means that there is a huge biomass in the substrate that can be used as a source of CO2. What's more, the anaerobic denitrifying bacteria can reduce nitrates, further improving the balance between NO3 and CO2 in a low tech planted tank.

I've done some reading on this, and here are some key components I've gathered:

- the sand bed must be at least 4" deep
- use of malaysian trumpet snails to regularly turn over the sand, preventing compaction and allowing fish mulm to be mixed into the substrate
- extensive root feeder plants to absorb any toxic (e.g. sulfur) buildup from the anaerobic layers
- minimize any disturbance to the substrate

What do you guys think about this idea?


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## PPulcher (Nov 17, 2006)

Interesting idea. Here are some random thoughts.

The amount of bacteria is also influenced by the nutrient source available, so having lots of surface area doesn't necessarily mean that you'll have more bacteria. There's more opportunity to colonize substrate/media, but the population will be limited by the nutrient source. 

Some plants prefer ammonium to nitrate, so they'll be competing with the nitrifying bacteria for it, shortcutting the conversion to nitrate. I've not seen this happen much in my low tech tanks (as I can measure nitrates) but it might be a partial factor.

As some plants and the anerobes in the deep substrate will be using the same nutrient source (nitrate) they'll be in competition with each other. I'm not sure how that would balance out.

If you decide to give this a try, I would be really interested in the results!


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## Tino (Sep 10, 2012)

I know I'm grave-digging here but has anyone given this a shot?
My cousin has successfully pulled it off in a much smaller scale (5 gallon guppy tank) and I find it fascinating that he has no filter and the tank looks stunning with healthy fish and amano shrimp in there. So now I'm wondering if I should give it a shot in my 75 gallon...

This is the website he got his info from.
http://www.wetwebmedia.com/ca/volume_7/volume_7_1/dsb.html


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## solarz (Aug 31, 2010)

Tino said:


> I know I'm grave-digging here but has anyone given this a shot?
> My cousin has successfully pulled it off in a much smaller scale (5 gallon guppy tank) and I find it fascinating that he has no filter and the tank looks stunning with healthy fish and amano shrimp in there. So now I'm wondering if I should give it a shot in my 75 gallon...
> 
> This is the website he got his info from.
> http://www.wetwebmedia.com/ca/volume_7/volume_7_1/dsb.html


Nice article!

I am planning to try this on my 79-gallon in a few months.

The type of sand could be important. Not sure how well it would work if the sand compacts.


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## Tino (Sep 10, 2012)

He used pool-filter sand if that helps.


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## BillD (Jun 5, 2006)

In the article, he uses the term PFS, but then talks of #35 size and even higher. PFS is #20, which is much coarser. Kind of casts the validity of the entire article into question.


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## fishyfishy (Apr 21, 2011)

I've read that article as well and do plan on trying it on a 150g that I'm planning. I've currently got a setup like that working great on a 5 gallon. 

In order to keep the sand from compacting you have to be sure that the grain sizes in the bag are the same. That way there is no chance of smaller particles getting in between the larger ones causing it to compact.

The only difference in the grain sizes would be the amount of surface area available for the bacteria to colonize. With a #35 you could get away with a slightly shallower sand bed vs a #20.


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