Thanks, I'm a little baffled by mine - nitrates test at almost 0. Good circulation and CO2 injection. 8 gr light cycle. My Co2 pressurised system isn't very well regulated however and fluctuates a bit. The needle valve is very hard to set in a position that is maintained - after a few hrs it either speeds up it slows down of it's own accord. Could the fluctuating CO2 be a problem? And should I invest in a better system?