Yea... You don't know exactly what is in them for one... Also don't know how much of what is in them. If you use them your plants will turn yellow and probably die after a while. How old are your plants and how many of the nutes have you used?
Edit: Read up... don't start in the middle of the thread either... All the info you will need can be found in these threads.
The AEROGARDEN!
Aerogarden, Round 2