I have a heavily planted 150g tank with Discus lots of flow and a sump with a wet/dry filter. I set my ph controller to turn on the co2 if the water gets above 7.4. This setting keep the plants happy and fish healthy- so far. Keeps the drop checker in a nice green zone at all times.
With good O2 from the overflow box(no scum) and trickling water in the sump things have been going well. I inject the co2 by using a lime wood air stone under the sump return pump. Creates a champagne like mist in the tank. There the fluval fx5 return splits the sump return flow mist into two directions.
BUT I am considering putting the ph controller on a timer to turn off at night since Tom Barr has some very good reasons why this should be done.
The Fraternity of Dirt # 115