First of all, 40 watts of light on a 45-gallon tank is weak indeed. If you don't plan to keep corals, then I wouldn't worry about it too much. This doesn't mean that you can't have coraline or anything like that, but don't expect such growth to occurr very quickly. Upgrading your lights might be in order, but it's not absolutely necessary.
Also, if you want another solution to your problem, I would recommend seeding your tank with a rock that does have a good amount of growth on it. I would find a fairly small rock packed with coraline (from a store or a fellow hobbiest) and stick it right in the middle of your rock or in an area of high flow to try to disperse the growth onto your existing rock.
i have a 45gal with 20lbs of live rock different shapes and types i had the setup for 6months in my 20 gal and switched to my 45gl few weeks ago is there anything im doing wrong because im all new to this type of setup thanks
