The sand from your sw tank, is it live sand or regular? You might want to test the salinity after the tank has water just to make sure that the tank doesn't have any salt remaining in the sand.
You can setup a nice planted tank without CO2. If you post a thread on the aquarium plants sub-forum here, there are several members who could help you with a low-tech
system. Basically, that is where lighting is the main source of plant growth, along with some other stuff.
We can go into that here, or you might be able to get more help at the aquarium plants sub-forum located here: Aquarium Plants