I'd say go for CO2! Reduce your photoperiod until you get CO2 on the tank. Remember, as long as there's light on, photsynthesis will be occurring, and if you're short on CO2 compared to the length of lighting, your plants will be trying to create sugars and grow without a key ingredient.
It like trying to bake a bunch of cakes. If you have a lot of sugar, flour, butter and chocolate, but only two eggs, how many cakes can you really bake?
Last edited by danakin; 12-13-2012 at 04:01 AM.