Hi there I've recently set up a pressurised system on my tank, and added some lovely plants etc etc, however i can't seem to get my drop checker to go green! i read somewhere that my size tank (40gal) should only need 1 bubble every two seconds, and I currently having it running at one bubble per second and my drop checker is blue. I have two different flows around my diffuser, one my external filter outlet and one from an extra powerhead, to blow the bubbles around the tank. Surface agitation is minimal and everything seems to be working fine, but aparantly there isn't enough CO2 in there!! Any ideas?