In this post, you will learn how to make your own coil denitrator for your freshwater fish aquarium. For those of you that are unfamiliar with the term coil denitrator, let me explain exactly what it is:

DIY Coil Denitrator

A coil denitrator is nothing more than a cylinder with a coil of tubing and some bio-balls. This device works, and achieves the same denitrification results as the more complex and costly commercial units, but much more easily, as well as naturally. A coil denitrator takes 5 to 6 weeks to cycle (yes, they cycle just like the tank). The quantity of product that is processed, (nitrate) is truly amazing, considering how once established there isn’t anything more to do! So how does this happen? As oxygen rich water is pumped into (G) and enters the top of the unit (A) it is forced to spiral down through the layers of plastic coil tubing (E) until exiting within the center of the cylinder (C). As the water level increases within the body of the unit, the bioballs (F) become host to the millions of colonies of bacteria that commence multiplying. As the water reaches back up to the top, it exits through the other fitting (B), the one not internally connected that runs back to your sump or display tank. So? So, as the water slowly works it’s way down the spiral, the O-2 is consumed by the AEROBIC (living only in the presence of oxygen) bacteria, the same ones that are in your filter and make all the life possible. Somewhere around 3/4th’s of the way down however, the O-2 levels diminish within the spiral, having been consumed by the aerobic bacteria higher up the coil. (D=Base)

Now that you have an idea of what a coil denitrator is, let’s get on with the project.

The Ingredients

4″ S&D PVC pipe (non schedule 40)
75′ 1/4″ tubing (get more as 75′ just fills the pipe and you’ll need more for plumbing)
4″ S&D cap X 2
3/4″ tee
3/4″ ball valve I had laying around
3/4″ to 1/2″ adapter
Three 1/8″ Barb x 1/4″ MIP
Two 1/4″ brass coupling
1/4″x1/2″ compression coupling

1. Cut the 4″ PVC pipe to 24″ (I used a saw but I imagine you could use your teeth if you don’t have a saw around)
2. Insert the airline tubing into the pipe (This is where most people will quit because I almost did. My recommendation is to wrap the tubing around the outside first so it takes the general shape of the pipe then insert it using both arms, one in each end. Use a clamp to keep the starting end in place. This will allow you to keep torque on the tubing as you wind it tight along the inside wall)

3. Next clamp the end piece so it doesn’t unwind on you.
4. Fill pipe with sweet bacteria condos of your choice (I used scrubbies)

It took 24 pads to fill it to the top.

Set this piece aside as we will now start on the top cap. Don’t forget to clamp that end piece because it will unravel on you!

5. Get out a drill and a universal bit.

You’ll use this to drill the inlet and outlet holes on the 4″ cap. So I wouldn’t drill holes too big for the 1/8″ barb adapters to fit, I traced out the bottom of the adapters using a sharpie.

Once the “threaded” end of the adapter has been traced out on the cap take your unibit and slowly drill out the holes being careful not to exceed the trace lines you made. I drilled mine just large enough to where I could screw my adapter into the cap creating a tight seal.

6. Flip the cap over and use plumbers tape around the threading of both adapters.
7. Place a 1/4″ brass coupling on both. Tighten the couplings to the adapters using wrenches. Mine were tight enough that leaks were not a concern in this low pressure application.
8. Place the third 1/8 barb adapter on the coupling mated to the inlet, again using tape on the threads.
9. Grab the pipe that we set aside ealier. Attach the airline tubing to the inlet barb. Use PVC primer and cement to secure the cap. Voila! Hope you didn’t forget anything because its sealed tight now!

10. To attach it to your setup will differ depending on pipe sizing and such. My return plumbing is 3/4″ pvc so adjust according to your setup.
11. Attach 3/4″ tee to 3/4″ ball valve using 3/4″ pvc, primer, cement.
12. Attach ball valve to 3/4″ to 1/2″ pvc adapter
13. Screw on 1/4″x1/2″ compressions coupling
14. Attach airline tubing to the compression end and run this into your sump

Finished Enjoy your new coil denitrator, your freshwater cichlids definitely will.