Excel is not always the best choice. It can harm plants. Co2 is much better. Laying the plants down horizontally so that they grow new stems from each node works well. I sometimes simply float them that way they gain co2 from the air.
I would go with what other people have said and use high light, high co2. If you already have a pressurized system you're good to go, otherwise put a bunch of DIY co2 reactors on.
I've noticed that many plant species I've kept point their leaves up towards the surface at the end of the day, even while the lights are on. I've read that this is a sign that they're pretty much done with photosynthesis for the day, and further light doesn't do much. That being said, I wouldn't do a 24 hour light period.