A DIY Nitrate Reactor for Your Aquarium

This DIY nitrate reactor is simple and inexpensive to make – and is great for keeping the nitrates in your aquarium below 2 parts-per-million.

I always struggled with keeping the nitrates in my 24g aquarium any lower than 12 ppm.

Two weeks after making this nitrate reactor, my nitrates fell to 2ppm. And for the past month they have continued to hold steady at 1 to 2 ppm.

Stuff needed to make the nitrate reactor:

  • Seachem De*Nitrate (every 1 liter treats up to 100g of aquarium water)
  • an empty mayonnaise jar with plastic lid (I just bought a cheap $2 bottle of fake mayo at the local grocery store and dumped the contents in the trash) – or any other jar with plastic; just make sure it’s large enough to hold enough De*Nitrate to treat your tank
  • a 1′ piece 1/2″ diameter PVC pipe (Home Depot, Lowes, or most any other local hardware store)
  • a 1/2″ PVC barbed insert x female adapter (FIPT x insert) (you will most likely have to order this online)
  • a 1/2″ PVC spigot x male adapter (Home Depot, Lowes, or most any other local hardware store)
  • a tube of JB Waterweld (Home Depot, Lowes, or most any other local hardware store)

The tools you’ll need to make it:

  • either a hacksaw or coping saw
  • a drill
  • 1/8″ drill bit
  • 1/4″ drill bit
  • 7/8″ drill bit
  • small piece of sandpaper (any grit)

How to assemble it:

  1. Use the 7/8″ drill bit to drill a hole in the center of the mayo jar lid. Lay the lid upside down on a piece of scrap wood to drill it so that pressing down on it with the drill won’t crack the plastic lid.
  2. With the lid still upside down on the scrap wood, use the 1/8″ drill bit to drill several small holes around the outer portion of the top of the lid. (These holes are how water will exit the reactor.)
  3. Use the saw to cut length of PVC pipe equal to the inside height of the jar.
  4. Glue the spigot end of Spigot x Male adapter onto one end of the piece of PVC pipe you just cut.
  5. Trim the opposite end of the PVC pipe just enough so that it is held snugly in place when you stand it in the jar an screw the lid down over the top it:with lid on
  6. Remove the pipe from the jar and use the 1/8″ drill bit to drill several holes in the bottom end of it. (The incoming water will flow down the pipe and then exit the pipe into the bottom of the jar.)
  7. Use sandpaper to remove any burrs from the bottom of the pipe, then use sandpaper to lightly scuff the inside bottom of the jar.
  8. Place some JB Waterweld epoxy on the bottom end of the PVC pipe, then press the bottom of the pipe into the bottom of the jar. Make sure the epoxy has stuck to both the pipe and the jar enough to hold the pipe in place.
  9. Place the lid on the jar so that it hold the pipe centered in place while the epoxy cures overnight.
  10. After the epoxy has fully cured, remove the lid, cover the top of the pipe with your finger, and pour the appropriate amount of Seachem De*Nitrate into the jar.
  11. Replace the lid and screw down until it is just snug.
  12. Screw the Barbed Insert x Female Adapter onto the top of the pipe sticking out of the jar until it is just barely snug.
  13. You are now ready to place it in your sump and attach your water feed to it making certain the flow rate through it will be no more than 50gph.

In my case, I tee’d a 1/2″ line off my main return pump line. And I stuck a cheap 2 Little Fishes Ball Valve in it to control the flow just before it enters the reactor.

I also used the spare space in the jar to hold a bag of granular activitated carbon and another mesh bag with some Seachem Phosguard in it.  That way I can get flow through all three types of filter media without have to use any electric pumps. (The fewer pieces I have to plug into my power strip, the better.)

To replace the Phosguard and carbon, I simply unscrew the barbed fitting, then unscrew the lid.

The De*Nitrate pebbles never need replacing, It is a good idea to rinse them off with clean water every now and then though. That way detritus build up won’t block the microscopic pores the anaerobic bacteria live in, and they can continue consuming the nitrates from your tank water.

Since De*Nitrate requires a flow of 30 to 50 gph to pass through it for optimal performance, I adjusted the ball valve to provide a flow of about 35 gph through the reactor.

Here are some shots of my nitrate reactor setup:

empty nitrate reactor
Empty nitrate reactor


media in reactor
De*Nitrate on the bottom, a bag of carbon and a bag of PhosGuard on top of it.


nitrate reactor in sump
Water flows down to the reactor, down through its center pipe, up through the media, and out the little holes in the lid.


nitrate reactor valve
Water is feed from my return line, though the ball valve, down into the reactor jar.