There could be several explanations for what you are seeing.
Plants can go through an adjustment phase, so that might be what you're seeing. But likely, there are a few other factors at play.
You lighting is way, way too low, unless you got very low light plants. However, I wouldn't think this wouldn't affect things immediately. You do need to get better lighting, I would suggest T8 lamps, and if you have the $, I would get the Zoo Med Max Plant Growth bulbs. They're expensive, but they work - and I tried several Home Depot/Menards/Walmart lamps. There's an old Watt per Gallon (WPG) rule (based on T12 lighting) that has been updated (somewhat) to reflect better lighting technology, but in general you should be able to keep most plants under "medium" lighting, which would be about 1-1.25 T8 Watts per gallon. I have 2x 32W T8s on my 55 and my plants do great. On a 30G, (I think) that's a 30" wide tank so (I think) you have to use 24" lamps - you would have to see what the watts are but I think whatever lamps you go with, use 2 and that will be plenty. Or you could add a couple more CFLs, but I am not the guys to talk to about which CFL is a good plant grower.
Most plants like established tanks, the waste from the fish is their food. I have gravel so the waste filters down deep and gets sucked into the roots, and I don't clean much more than the top 1" out of 3" of substrate. With sand, the waste doesn't make it down to the plant roots quite as easily, it just sits on the top. So your plants will take longer to establish and spread roots (because the substrate is more compacted) but they eventually will take hold and adjust to the tank. You might want to buy a pack of root tabs and put one under each plant to give them a little boost.
From what I remember reading, you would only need CO2 when you have very high lighting and are experiencing an algae bloom. A CO2 planted tank is quite a balancing act from what I understand, and while I never did CO2, for a while I used a carbon supplement (Excel) and had good growth and good algae control. Generally, unless you have 'too much' light, you don't need CO2, I believe.
Anyone feel free to correct me if I'm wrong...