what is the pH of the water that you're feeding them with? for soil you want to give them water with a pH of around 6.0, if you're using tap water it generally is higher than 8.. you can pick up a pH reader for 50-75 bucks on average, or find some pH test strips at a local store.. in the past my plants grew small due to ph being off, so I can relate. they sound like they're doing alright for a couple weeks..
test pH and let us know