Hello Cat,
First things first...check what your wattage to water ratio is, usualy for planted aquariums is 2 to 3 watts per gallon of water, the bigger the tank the farther the light has to travel to the plants. Second when you moved your plants from your 30 gallon tank did you trimmed the roots a little?, doing this stimulates the growth of them ensuring the plant assimilates all the nutrients it needs to grow and be healthy. Also you have to look into your local water supply, e-mail your local water company and asked them for a chamistry report, it should break down all the nice info such as, what concentration of chlorine and chloramines it has, potassium, zinc, iron things like that. Also you want to look into your Carbonate Hardness which is display as Kh. The softer your Kh degree is the easier it will be for you to maintain your PH stable in your tank. I notice before I added the live plants my PH in my tank ran at around 7.5, but once I started CO2 fertilization it lowered the PH in the tank to 7.0 which is neutral, I did noticed some of the fish had a hard time with this. Anotherthing yo want to be careful with is overdozing trace elements into your water column. Pay close attention to this, beacuase if you don't you will be figthing alge always.
Hope everything works out, and good luck.