My friend Matt flew in yesterday from Arizona. We ended up going to Big Al’s pet store. We where looking at the planted tank accessories, and noticed that they want $130 for a CO2 Reactor. We put one together for under $40.
A CO2 Reactor is a device used with planted tanks that will help push Carbon Dioxide into the aquarium water. Plants LOVE carbon dioxide. It is a major fertilizer.
Here are the $40 worth of parts I needed to make my Homemade CO2 Reactor. These parts include a couple of Siphon aquarium Cleaners, some Bio-Balls, airline tubing and couplers, and an Eheim Filter part I used for a water line splice.
We disasembled one of the aquarium siphons and attached the hose to the other siphon. These are Python brand siphons, they are fitted by compression – no glue, so just pull hard, they will come apart. There are enough bio-balls inside to completely fill the tube.
Here Matt and I are leak-testing the Do It Yourself CO2 Reactor in my bathroom. We hooked it up to my Ehiem Canistor Filter, ran it into a bucket of water, and turned it on. Can you believe? It works! Only a minor leak too!
Here you can see the CO2 Reactor installed on my fish tank. I wanted it to be visable, so I mounted it right up front. I just think this gadget looks so darn cool!
More complete assembly details to be coming soon. 
Is it possible to just put the bio-balls into the canister filter and get the same results?
Janet,
I had originally fed the CO2 into the canister filter, before I build this reactor. This made the filter noisy, as the impeller chopped the CO2 bubbles up really small. It would also sometimes cavitate the impeller, and the whole pump would stop pumping.
Injecting into the filter is quite effective, as the impeller makes the bubbles very small so they have higher surface area, but the fine bubbles do survive out into the tank, float to the top, and pop, getting lost.
Doing what I did in this post gives 100% CO2 injection (dissolved) without making the canister filter noisy – assuming of course you don’t put so much CO2 into the reactor that it gets pushed out the bottom.