Deep Sand Bed - (FW)

[flukes]

Hi guys just writing with something that i have been wondering for a while. When i started researching marine aquariums one thing that is used is a DSB ( Deep sand bed) which basically amoung other things removes nitrate.

I started thinking why can this be replicated in a FW setup? As i know nitrates are a royal P.I.T.A and one of the main reasons water changes are needed so frequently.

Now this doesn't have to be in the display tank, a remote deep sand bed can be made under the stand and pumped back into the tank. Or maybe even a canister filter could be used.

Surely a FW DSB/RDSB would have the same anaerobic properties for denitrifying bacteria, as a SW tank.

They only thing i can think of is that a FW tank would not have the same life forms that sift through the sand bed, but i am not sure if this would be a problem as i have seen bucket used as RDSB's where it wouldn't have the same critters as in the main display.

Just wondering has someone tried it?

I would guess it doesn't work otherwise someone would already be using this method but i just would like to know the reasoning for it not working.

[Robdog]

I have thought the same thing Scott when I started my first marine setup. It's probably something best answered by the bacteria nerds among us.

By the way, by "critters" do you mean the worms and pods and other little crawly things that you find in a marine substrate??? I didn't think these had much to do with the removal of nitrate, more the bacteria involved in the slow tranferring of water from an anaerobic area to an aerobic one.
I may be way off the mark :ug

[flukes]

Yeah i couldnt see how it would make a huge effect, but thats about all i can come up with. I dont have a FW setup to try it on atm, but surely someone would have already tried it.

[Robdog]

When I did my little marine tank I considered the DSB but wanted to make sure I had as much water as I possibly could so I left it out. I did consider something like a plenum setup with a few UGF plates and then substrate over the top. I think this would have been better as you don't really need the substrate depth that is required for a true DSB.
It would be a good little experiment

[fiftycal]

What are the concentrations of Nitrate in SW systems as opposed to FW systems?

IIRC there is a commercial nitrate reducer that uses some form of sulphur based balls as media. Perhaps the bacteria require some sort of sulphur source? I am not very familiar with SW so I have no real idea lol

[Baro]

I recall reading a post about this on the internet, sorry can't remember the forum. One of the key differences are the invertabrates in a SW systems that churn the sand and prevent it from going completely anaerobic. And no one seems to be able to get one to work in a freshwater set up, or with limited success.

In a planted tank the plant roots prevent the substrate becoming too reduced (total lack of oxygen). If conditions become too anaerobic Hydrogen sulphite (highly toxic rotten egg gas) is produced rather than nitrate being reduced. I guess a planted tank is the freshwater equivalent of live rock and deep sand substrates.

I think fw is more tollerant of nitrate than sw.

Denitrification can use carbon or sulphur as the energy source. Homemake denitifiers often use alcohol eg vodka, as a carbon source. Commercial equpment uses powders, biodegradable plastics or sulphur. If sulphur is used sulphuric acid is used which then passes to a neutraliser of calcium carbonate which harden water, not the best for soft water fish such as discus. The water flow/food/nitrate load must be carefully balanced in these filters. Too much water flow and the anaerobic bacteria that do the reaction can't get established as there is too much oxygen. Too little water and they consume all the carbon and start producing sulphur dioxide. If there isn't enough carbon they also produce sulphur dioxide. The systems are best monitored electronically to keep the system where nitrate is denitrified and not doing something else.

I use an aquamedic denitrifier, with a probe, waiting on the Redox (mV) controller.

Another difference is that many freshwater bodies have clay/mud substrates rather than the reef's sand.

I hope this helps.

Cheers,

Paul.

[flukes]

Thanks for that, thought it was something to do with churning up the sand bed.
Now i can stop wondering. :wink: