edges of leaves turning brown :S
When you say "40W fluorescent bulb", do you mean CFL? And if so, is that "actual watts", or is that "equivalent watts", making it actually a 13 watt bulb?
The reason I ask is because that plant is spindly. If you had a 40 watt CFL (150+ "equivalent watts"), that plant would be doing better.
Your next problem is that if you put the right amount of light in there with your plant, you'll burn it to death. One little 12v fan operating on 7 volts is no where near enough to vent the heat from the light. And that looks like aluminum foil, which is not a "Planet Skunk" approved reflective material because it causes hot spots. So if you up the wattage, you'll burn the plant to death even faster.
Your next problem is only watering once per week, and not having any perlite (or vermiculite) in the soil. Watering should be 2 or 3 times per week, depending upon soil and container. Watering is done when the top 2 inches of soil in the container is dry. How dry is the soil when you water, and do you have drain holes in the container?
Your next problem is that you only have one plant, and I'm assuming that you don't know what sex it is. Call it a 50/50 chance that it's a male, and if it is, your growing compost.
Now, on to your original question: The tips are burning probably from the heat inside. And you don't even have enough light to begin with. I think that you need to start over with a new grow setup.
"No, the voices in my head didn't tell me that I'm the chosen one...I figured that out on my own."My Avatar Grow.