If you have 18 watts over 23 gallons, that's pretty low light, but you should still be able to grow some plants.
Try Anubias, Cryptocoryne species, Java fern, Java moss, maybe Amazon swords and, if your water is on the hard side, Vallisneria.
Your tank inhabitants might produce enough waste to feed the plants, but if they don't, you can add a general fertiliser. With that level of lighting and those plants there shouldn't be any need for carbon addition.
Give them something like 8 hours of light per day and see how things go.