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Old 08-19-2003, 11:14 AM   #1
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Coil Denitrators

Has anyone had any experience using coil denitrators on a freshwater tank? It seems pretty straightforward, and safe as long as you feed the output back through a biological filter, but there seems to be alot of distrust in them whenever I read about them.
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Old 08-19-2003, 02:48 PM   #2
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the distrust stems from the fact that dinitration can produce toxic amounts of Hydrogen Sulfide gas ... H2S is far more toxic and ammonia or nitrite.

I think H2S production results from the too complete of a denitration, all the oxygen is consumed, then all the nitrates are consumed and finally you get some really tuff bacteria that do a further breakdown and their waste product is H2S.

So the trick is balancing the flow rate with the reduction rate... too much flow results in little denitrafaction, too little flow results in H2S production.

A safer form of denitration is aerial growth plants, like duckweed, ludwiga, hygro, etc ... these plants when grown rooted in water but exposed to air consume large amounts of nitrates and turn it into biomatter, then all you do is trim the biomatter (leaves) from time to time and nitrates are removed for good.
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Old 08-19-2003, 03:18 PM   #3
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I plan on having just that sort of setup with some philodendrons and other emmersed plants. I was just curious why these denitrators aren't more common on FW tanks- they seem like they'd be a cheap and easy way to cut back on water changes, once you got it running right.

Do you think bubbling an airline through the effluent from the coil (in a separate chamber) could remove the H2S before the water was returned to the tank?
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Old 08-19-2003, 03:24 PM   #4
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it would be safer and more effective to give the coil an accelerated flow, so that not 100% of the nitrates are removed ... as for aeration, instead of an air stone, make sure the water returning produces or encounters turbulance ... it is the turbulance bubbles create that exchanges gases, not the bubbles themselves. have the stream of water drain over some exposed rocks would work better than an airstone.

fw fish have high tolerance for nitrates. your plants, combined with even a mildly inefficient denit. coil should provide very safe levels.

does your tap water contain high levels of nitrate? regular water changes should keep levels low as well.
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Old 08-19-2003, 03:46 PM   #5
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Awesome!

I haven't tested my tap water- I don't even have water in my tank yet- I was just curious about it. Now I think I could really use it to help reduce tank maintenence though, and running the effluent over rockwork as opposed to bubbling it. With a shorter coil/faster flow, how serious is the risk of raising the nitrite levels in the tank? I would imagine that the amount coming out of the coil would be way below the filter's capacity, but I wanna be sure.

Also, is a simple coil of tubing sufficient to use for denitrification? I've also seen more elaborate setups where a coil empties into a sealed, anaerobic chamber full of bioballs, but I don't see why that would be superior to a little bit longer of a coil.
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Old 08-19-2003, 08:37 PM   #6
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as for the length of the coil, longer is better.

try for at least 25 of small tubing... 1/4 ID tubing at my ace is $0.20, so 25 feet of it would only be $5 ... it is the semi ridged white stuff, not the clear - should hold up to being coiled better than the soft clear stuff.

most of the designs i've seen use a 4" PVC pipe to form and contain the coil and like you said, bioball media.

the objective of the long tube is to deplete the oxygen, releasing a stream of nitrate rich oxygen poor water in the main biochamber, where the bioballs play home to the denitrafication bacteria. Because the volume is much greater, the water moves a lot slower in the biochamber, and thats where the bacteria want to grow. Water then exits the biochamber and is remixed with tank water in a sump, or over the rocks like we discussed.

I speculate that the tube and extra biochamber take some of the guess work out of determining flowrate and tube length. a coil-only system would need an incredibly low flow rate of only a few gallons per hour, due to the small volume.

adding the biochamber and biomedia provide an enormous increase in the surface area, allowing more bacteria to grow and process the water faster.

Check out this link for more info
http://www.thekrib.com/Filters/denitrator.html
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Old 08-19-2003, 08:47 PM   #7
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Check this out... it works but, it is real tricky... by hm hm yours truly

http://www.aquariumadvice.com/viewtopic.php?t=2362
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