I'm not sure how effective this is going to be for anyone else but it is working great for me. Not sure if you could actually call this a reactor but does the same job.

Bit of background:
The CO2 ladder diffusor I got with my CO2 kit was too big and didnt do a very good job. Needed about 4bps to get the drop checker into the green/light yellow.

I took this out and injected the CO2 straight into the outflow pipe from my canister filter. This worked better but most of the CO2 just shot straight through and out the spray bar.

3rd attempted was made by putting some filter foam in the outflow pipe. This difused the CO2 better but slowed the water flow down by loads. Also the foam kept getting pushed along the pipe where it then blocked the spray bar and cut the flow to almost nothing.

I did plan on building an external CO2 reactor but was worried about it leaking and also to buy the parts locally was not that much cheaper then buying a premade reactor.

What I needed was something in the tubing that would not move, would not slow down the water flow and would do a good job of disolving the CO2.

What I came up with was really simple and suprisingly works really well. I'm not using 2bps to keep the drop checker in the yellow.

All there is to it is a short peice of tubing the same diameter as the out flow tubing/ I made mine about 2 inchs long. Then I just cut this into a spiral with a short "Ring" left on the end to hold it tight into the tube.

I put two into the outflow tube. One just after where I inject the CO2 and one about a foot along the pipe just before the spray bar. I do get some CO2 mist but I'm sure if I injected the CO2 further back on the pipe and put a couple more in it would disolve almost all the CO2.

Pictures:

Take 2-3 inch of tubing and cut into a spiral. Leave a ring at the end and cut a straight line in this (so it wil slide into the outflow pipe).


Cut two-three more spirals into the tube.


You now need to put it into the outflow tubing. I didnt use anything special. Just stretch the spirals out and shove the "ring" end in using anything long that comes to hand. Make sure the ring end goes in first with the spirals going in the direction of the water. At least with the tubing I have it tends to "stick" together so it holds in the pipe where ever you leave it. You might need to re-arange the spiral ends a bit as they tend to get bunched up and completely block the tube. I used a bit of stiff wire to push the ring end in and move the spiral bits around to make sure there is plenty of water flow.

If anyone else wants to give it a try I would like to hear the results. Like I said it works for me, no slow down in water flow and good CO2 amounts being disolved but I havent tested this with any other kit at all.