What is your tank equipment? filter? total flow gph?
According to James's Planted Tank.net the cause of the problem is:
In a high light tank it is an indication of low or fluctuating CO2 levels or not enough water circulation around the plants. In a low light tank it is often due to changing CO2 levels.
If you got your co2 worked out, I think you have a low flow problem in the tank.
I would recommend leaving your co2 constantly on like 1-2 hours on before the light goes on and 1 hour before the light goes off.