Well, I finally got my CO2 canister today and I wil be building my DIY reactor tomorrow. I'm using this reactor http://www.gwapa.org/articles/inline_co2_reactor/ on my Eheim 2215. Just to be clear on one important point. I have absolutly no intentions of placing this thing on the intake of the filter but rather on the return. Anyone got any thoughts on placing it on the return line?