denitrators: useful, waste of time, dangerous, etc?

I have read a bunch of opinion of denitrators (DIY ,etc). Some say they are useless. Some say they are dangerous. etc.

I would like to quantify the opinions with a poll. assuming I do it right.

I have a freshwater aquarium fighting rapidly rising nitrates. 3x water changes a week to keep it below 40ppm is getting old. I think it is being caused by some of my plants. They routinely shed leaves which usually collect in the corners unnoticed until they rot.

I just found the denitrators and cant decide if i want to build one or not. I got a pretty nice design that should eliminate the deoxygenated water problem in mind using tubing 2 pvc pipes and an airstone.

Hmm toy in the results at the moment.

Here is my idea for a denitrator. I am designing it around a 20G long tank on a 3 ft stand. It's all in my head so bear with me. It basically boils down to a vertical coil denitrator that uses a bubble column to return the water to the tank. Again I have not even built this yet so it may flop big time, give me your opinions on the feasability

Approximate Parts:
1/2" ID pvp pipe the length from floor to about 1/2 inch above top of tank (CPVC, or some other safe rigid tubing., clear would be cool if i can find it)
plastic primer and welder (if safe for fish?)
a long length of flexible tubing
a 1-2"(?) pvc pipe of equal length as above
at least 2 pipe terminator caps
maybe a few other attachments (elbows, etc)


First cap the bottom of both pvc tubes.

The core of the system is the 1/2 pipe. take the tubing and wrap a coil around it. it will proably be possible, but harder to prime, to double or triple the coils if you need more tube length.

The top end will syphon water from tank which will of course coil its way down the pipe. The bottom end of this tube will connect to the pvc pipe using the proper connectors. To monitor flow maybe put one of those IV drip indicator tube thingies. You might need one of the flow control connectors

With this setup you should be able slowly syphon water into the sytem and have it stop when the waterlevel in the 1/2" PVC is equal to tank. Now to return the water to the tank.

I am a bit fuzzy on the details on the output spout but will probably consist of 1/2 elbows and should probaby spill into the inlet side of your "hang off the tank" filter. This way the biofilter can handle any imbalances that could be caused by the denitrator.

To actually make the water flow I plan on dropping an airstone into the vertical 1/2" pipe. This should create the same flow as underground filtration as well as reoxygenate/de-CO2 it to some extent. How far down will have to drop it down will have to be toyed with. Too far and bubbles go back up the coil, too high and you dont move enough water. Instead of using a flow control you might be able to use the airstone position.

The larger pipe with a cap will be for safety. After everything is put together and ready to go the larger pipe is slipped over the small pipe and coil. Incase the coil leakes pops loose ect. the large pipe will fill with water and should equalize syphon rather than syphoning the entire contents of tank into floor. Also the intake could be mounted like 1/2 below the water surface for an extra safety measure. In case there was a leak that outer pipe couldnt handle the syphon would stop when the water dropped 1/2 inch.

All I havn't really figured out yet is an easy way to clean the grundge out of the bottom that will eventually accumulate. But from what i've read having to clean a denitrator basically resets the cycle in it.

Of course all of this probably will mount to a wall or to the stand and sit with the end on the floor.

Ok got the parts. I decided to go with a 3/4 inch PVC for the core. the 1/2 made the coil too tight and was crushing the tubing. Also i decided to use the stiffer milky polyethylene tubing because even going around the 3/4" the vinyl was getting flattened. I also found a nice little connector the peth tubing slides in securely without any tooks. It can also be removed just as easily (sort of a chinese finger trap contraption) I drilled and tapped a hole in the side of the pvc pip for this connector to screw into. I also left layered on a good gennerous layer of silicon caulk around it just in case. Also solved the "clean the gunk out of bottom" problem .. I found a screw on cap and a cementable connector. this will work nicely.

I have cemented all the parts together and I am leak testing it (filled it full of water, sit it in a bucket, and wait) if this shows no leaks im going to start winding the tubing.

Also, I belive I have decided to use about 100' of tubing. This is because I have a feeling my flow is going to be greater than prescribed in all the other plans I've seen. So, I need more room for the colony segregation.

Once completed, cycled, and verified to be working properly (mid may/june?) I will post my complete plans with pictures. I will also try to post status reports periodically.

Also, while I was thinking of the proper bubbleing apparatus to use for this, Its similarities to a protein skimmer became apparent. I have a new question. How much salt has to be in the water before protein skimming becomes effective? just an academic question. My tank is freshwater (some fish can live in brackish, but not all)

I'm also contemplating a way to create a self starting syphon. got something stuck in my head trying to get out. must.. find .. old .. Mr.Wizard episode with the bendy straw and funnel.

week 5. its finally starting to denitrate. whooh. the effluent im at about 20% -50% of what the main tank is showing. nitrates are no longer skyrocketing whooh. i can keep them under 40ppm with bi-weekly (once per 2 weeks whatever the prefix) vs 4x a week water changes .

the visible bacterial plaque is only about 10% down the coil so 0 nitrate effluent is in forseeable future.

Also, ive got an interesting side effect. i dont know if it doing anything, but i am getting a bacterial coating on the inside of the pvc return tube that is a very appealing shade of blue green. I am assuming this is an aerobic bacterial since the water is being returned with a 3 ft column of very fine bubbles. I'm hoping that this agitation will force the dissolved nitrogen from the denitratification process as well as any of the hydrogen sufate that might be generated before it returns to tank. I'm also thinking that the unexpected film might help with that too. no evidence yet. but we will see.