Short of taking it to a professional there isn't much you can do....BUT....... If you can get some touch up paint, and the smallest sharpest brush you can find (you can even use a toothpick), you can slowly fill the chip with touch up paint without gobbing it on and creating an obvious eyesore repair.
Pick up a small amount of paint and touch the middle of the chip. Do this once, don't just keep adding paint....Let it dry and do it again. Repeat this until you level the chip with the surface of the tank. This will not fix it but it will make it less obvious until you choose to have it repaired. Do it carefully and you may be happy enough with your work to leave it be!