How many watts does he have? Most important in order goes a bit like this:
Light
CO2
Macro nutrients (N, P, K)
Micro nutrients (e.g iron)
With enough light, coupled with the second biggest factor CO2, they can't go wrong. What kind of plants are they looking to grow? Ones like java fern, java moss, most stem plants are less demanding on the light. Red plants and ground cover plants need a lot more as well as some others.