DIY reactor, its great. And not terribly expensive. I built one myself. I used a hacksaw, some pvc primer, glue, and cement, and some clamps to make sure the pvc didnt expand out.
Heres a link on APC http://www.aquaticplantcentral.com/f...ht=DIY+reactor
Here's Rex's guide Rex's Guide to building a CO2 reactor
They both work on the same principle pretty much. For the inlet in the PVC just drill a hole smaller than the co2 tubing. cut the co2 tubing at an angle and thread it through. Also if u have any threads on the PVC make sure you use teflon tape. Cut the output tubing in half with a razor blade and put the barbed ends of the reactor through the filter tubing. It helps tremendously if you let the ends of the tubing set in some hot water for a little while before trying to put them on the barbs. I like the inline because you have less junk in the tank. I have noticed a huge difference in the size of leaves in plants. You can check out my journal, I have a picture of some Rotala with tiny 2mm -3 mm leaves in the midsection, than when the co2 was put it, I got leave of about 3/4 of an inch. I went from a simple diffuser with one of those spiral things in the middle and a ceramic disk at the top to an inline DIY co2 reactor.
I'm still perfecting my reactor but it seems to be working fine as it is, even though I have it on the intake side, which isnt as good as the outtake because it can limit the flow into the filter. I get a fine mist out of the filter outtake, which I hope to change, but am having second thoughts about that after what MAHA said. I use pressurised, but you might be able to use DIY in it. I strongly recommend pressurised though. I got an AZOO regulator for about 50-60 bucks. The most expensive part of pressurised was the tank for me, but it lasts a while.