If you have to use walmart, you can start with a tomato food, but it really isn't ideal for your plants, and don't forget to use LESS than the label says until you know your plants can take it. Better, go to a garden store and look for a fertilizer with a higher FIRST number on it- that is a 'grow' fert. Don't ever use orchid or azalea food, or miracid!
Definitely take some time to check out what hydro shops stock, because those are MADE for cannabis.