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.
Ah good a fellow wet dryer!
With a wet/dry filter co2 cannot build up overnight. They are too efficient at gas exchange
That being said, with discus and a slightly green dc, i might consider leaving co2 on 24/7.. they are a temperamental species for sure. Ph being less important than kh and gh. But still..
That being said u are correct turning co2 off at night is advantageous, with a ph of 7.4 its not that important, ur bacteria is functioning very efficient at that level. Below 6.4 ph is when bacteria becomes mostly useless, which is the primary reason to turn off co2 at night