Have you read Tom's article on a non-CO2 tank?

Non CO2 methods

Flourish Excel is an excellent alternative to CO2 injection in a low light tank. Demands for nutrients and CO2 is reduced with less light so you can get away with lower carbon levels.

Also with the reduced light comes less fert dosing. You can cut back the days you add ferts to once or twice a week per ferts.

13w is a little low, try 2 10w-13w bulbs. 2wpg in a 10g tank isn't alot of light and is still considered low light.