[chagovatoloco]

I'm not sure their are any draw back on a timer for co2, but there is a lot of debate on this.

 

[chagovatoloco]

Plants only consume co2 during their photo period, at night they stop consuming co2 and start consuming oxygen. So their is a danger that the oxygen levels might run low at night and kill fish, and since it dose the plants no good at night any way many just turn it off.