Write an article based on this "Purchase and test out highlighters to see if they glow. Fill a clear container with water. Take the ink tube out of the highlighter. Place the felt stick and ink tube into the jar. Shine a black light at the water."
Not all highlighters have the glow-in-the-dark quality produced under a blacklight, so draw with them on white paper first and run a black light over to see if they do.  You can use any color, but yellow is the most likely to glow in the dark consistently. Any brand of highlighter should work, but you can try neon colored markers of a non-highlighter variety as well. It is easiest to see if they glow in a room that is completely dark, allowing for no light pollution. Tonic water isn't the only substance that contains light-producing phosphors — plain old highlighter markers work in a similar way as well. Start (as before) by filling a clear container like a glass jar with water. Note that this method will ruin your highlighter marker — it won't work when you're done. If you just drop a highlighter into a jar of water, it won't bleed ink very quickly through the strip of felt at the tip. Instead, you'll want to take the entire ink tube out. To do this:  Uncap the highlighter. Use a pair of pliers (or your hands if you don't mind getting messy) to pull the felt out of the tip. Use pliers to pry off the bottom of the marker. Carefully pull the ink tube out, taking care not to spill or mark your clothing. Drop the felt, the ink tube, and any other ink you can get out of the marker into the water. The ink should bleed into the water, changing its color. Cut or break the ink tube if needed to get the ink out. Mix the water well so that the color is even. You can leave the ink tube and felt in the water when the ink is done mixing or you can fish them out — it's up to you. Just like with the tonic water method above, a dark room and a black light will make the highlighter ink in the water glow brightly. You can also tape a flashlight to the bottom of the container to make a colored light (however, the "neon" effect you'd get with a black light is lost.) Unlike tonic water, the glowing water from this method is not safe to drink.