30" tanks are problematic for standard off the shelf fixtures. There are 30" flourescent bulbs/tubes/lamps, but they don't come in the variety one can get in standard 24" and 48".
A single T5HO or two T5NO lamps should suffice for either tank, but will of course be more light, at the substrate, in the 20L.
DIY using four 23 watt, daylight, small size, spiral flourescent bulbs will work fine. If you're into DIY LED is a great way to go.