Most everyone target a CO2 ppm of 20. The reason for this is to give the plants just enough, no excess. ALgae tends to creep in on excess. Assuming that you have high light and abundant ferts, 30 ppm might be good for you. Like Blinky said, watch your fish. If you are home one day and want to play with cranking it up, just stay close by to monitor your fish. Remember that cranking up your CO2 will cause your Ph to drop. Dropping Ph too quickly will NOT be a good thing for your fish, so you have to take that slowly.
As for floating plants, the gas exchange at the surface is far different than when the plant is sumberged, hence the growth.
As for floating plants, the gas exchange at the surface is far different than when the plant is sumberged, hence the growth.
