That's allot of light for a 20gal long. Its the light penetration that is most important in matching the right light for a tank. A 20gal long is a short tank. It wouldn't take much to get good light penetration. To save on money I would replace the 55w PC bulbs with some 36w PC bulbs. You might get by with that but that's still allot of light for a short tank.
Hawk |