I've got a 45-50 litre heavily planted tank. The substrate is just sand, there's a 36 watt bulb on it, which is on for 8 hours a day. I've bought some fertiliser, but haven't put any in yet. Basically I want to know how little I can get away with - I was thinking that maybe the short hours the bulb is on, plus the fact that there's hardly any surface disturbance, and no airstone or anything, might mean that I could get away with not having a CO2 system?