Kelp and molasses is comparing apples to oranges. Kelp is a fertilizer. Molasses provides little to the plant directly, other than a few micronutrients. What it does do is feed the microbes in the soil, which then decompose the organic matter in the soil and make nutrients available to the plant. There's two issues, the microbes basically use up all the sugars within a day or so and then their numbers crash back to normal levels, and if you're using synthetic nutes, it's also not that effective. One more thing, if your using it outdoors, it has a tendency to attract pests (possums, raccoons, rats, dogs, etc.). I've used non-sulphured molasses several times, and really saw no appreciable difference in plant growth, yield, or bud production.