Your plants will need root tabs in gravel since gravel is inert. Seachem makes a good root tab. As for PetCo and Pet Smart you just have to be careful you buy actual aquatic plants, they sell many that are not fully aquatic so if in doubt write the name down and go research it before buying it. Anyway I've seen Swords, Crypts, Java Fern Wendilov, Bacopa, and even some Dwarf Hair Grass when I was in getting cat food the other day. What type lighting do you have? Lighting will determine what type plants you can grow. Although the first 3 plants I listed can do low light. Also if they have any water sprite or wisteria you should get one of them. They too will work in lower light tanks.