Light causes algae, C02 grows plants! 2 x T5 is more than adequate to get a lush growth of any plant at that depth of water,
You need to get more gas down to the substrate.
General statements like this are just IMO incorrect and misleading. First off light grows plants as well, we can have too little at times. If the plants are growing slowly then sometimes a little extra light could lead to better organic uptake, better growth and a cleaner tank. This extra light might be in the form of a 1-2 hour burst that might have a more positive aspect on plant growth than a negative aspect on algae. It really depends on the setup,
Also the comment about the 2 x T5 being enough light for that depth was made before even knowing what kind of T5 the OP was using. As we know now this varies tremendously by model/manuf.