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chrismrutherford 05-06-2007 04:32 AM

Home Made Nitrate Filter?
I may have just figured out a way of lowering nitrates in my tank. Having viewed some commercial biological nitrate filters it is clear that to remove nitrates you need anaerobic bacteria. With a normal external canister filter that circulates water from the main tank at a relatively high rate you have too much oxygen for the anaerobic bacteria to thrive.

In order to breed the anaerobic bacteria you need a flow rate low enough to guarantee that your canister filter contains oxygen depleted water. The commercial systems use a drippier to feed the filter with drops of water, where the flow rate is 1 - 4 l/hr ( 0,25 - 1 gph) for a small tank (5 L canister) and 12 - 30 Liter/hr ( 3 - 8 gph) for a large tank (30 L canister).

Building a drippier system is complex but putting a timed relay on a normal canister filter isn't. I set a relay timer circuit to 90 seconds off, 2 seconds on. I measured the flow for one pulse to be 100mL, which averages out at roughly 4 liters per hour. I used a spare AVEX 600 external canister filter with a volume of 2.3 Liters. I replaced some of the filter medium with porous clay pebbles to increase the surface are and encourage bacteria growth inside the pebbles where the oxygen will be at its lowest. I used a Velleman adjustable interval timer placed inside a plastic box with a 12V wall mounted power supply.

I took some water out of my tank with quite high nitrates and put it in a test tank. I then left in with my anaerobic filter for about 1 month. When i measured the Nitrates they had fallen to zero. I have since connected the filter to my main tank and I'm eagerly awaiting the results.

Has anyone tried this before? Will it work on my main tank? What removed the nitrates from my test tank?


Chris R

jones57742 05-06-2007 06:02 AM

Re: Home Made <span style=

Originally Posted by chrismrutherford
Has anyone tried this before? I have not.
Will it work on my main tank? Most probably yes.
What removed the nitrates from my test tank? Anaerobic digestion bacteria.


You have done some "very, very good thinking here".

I am concerned about byproducts of the anaerobic digestion (specifically nitrous oxide and nitrogen dioxide: hydrogen gas production is a very small probability).

IMHO if you observe your fish beginning to experience any stress I would "unhook it".

If this works you will "have really come up with something" here!


Mrmofo 05-07-2007 03:51 AM

1 month the water could have stablised by itself?

jones57742 05-07-2007 05:41 AM


What do you believe may have caused the reduction of the nitrates?


Falina 05-07-2007 06:30 AM


Originally Posted by Mrmofo
1 month the water could have stablised by itself?

Possibly if you have certain plants. I think wisteria "soaks up" nitrates.

Robnjo 05-15-2007 12:56 AM other good cheap way is to run a Fluidized bed as slow as you can without the sand all together, works a charm :wink:

caferacermike 05-16-2007 08:37 PM

Just search for "denitrator coils" online. You'll find thousands of links on how to build your own aneorobic denitrator. Essentially you get about 200' of 1/4" ice maker tubing. Find a manufacturer that ships it on a plastic roll. Bam!!, you have a denitrate coil. Hook up a small pump and a 1/4" ballvalve. Set it up so that water just drips from the exit tubing. Folks say once it is set to put a small amount of table sugar in the entrance of the inlet, this will get the proper bacteria going sooner. I've also read of folks doing just that but then shut the pump off after about 2 hours. In theory this traps the water in the end area of the coils and speeds up the aneorobic reproduction. The idea is that regular bacteria begin to break down the waste and different types of bacteria grow along the entire length of the tubing, the longer the better. These take about 6 months to begin "working" and will go out of whack if bumped, removed, or if air enters.

chrismrutherford 07-07-2007 11:35 AM

Well it's been about 2 months and I can positively say that my timer system works. Indeed my smaller tank with more fish has lower nitrates than my large tank with less fish and more plants. I'd say that is pretty conclusive. I might make some final readjustments by to increase the off time to 5 mins and fill the canister completely with clay pebbles.

The fluidised sand filter idea is great too, i might try that. I have fluidized sand filters and they work great for aerobic bacteria.



porksnorkel 08-19-2007 05:38 PM

soooo....why not just get a flow adjuster? and how is this differnt from a sump or any other type of wet dry for biological filtration? anyone think this constant on/off might burn this cat's pump up?

anyone gotta link on the technical side of removing nitrates? maybe that's where i'm confused.

caferacermike 08-21-2007 04:06 PM

Yes I would avoid the stop start of the pump UNLESS it is a DC pump. It would be far easier to plumb the system in using a low GPH pump a "tee" and a valve. Put the tee inline just before the "contraption" and then use the valve to allow the water to flow out the side adjusting the "contraptions" flow however you wish. The best method I've ever seen used a large acrylic tube, think a pail of water, a 1/4" threaded valve underneath and a pump pushing water into the bucket. From the bucket you have another pipe thread into the side near the top, this then exits to the sump below. The pump pushes water up into the bucket, the water fills it to the top and overflows back to the sump, however gravity pushes the 1g or so of water in the bucket down the 1/4" valve into the "contraption". This allows you to fine tune the system all the way down to a drip without fear of burning up a pump.

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