that sounds like a 20 watt 24" t12... if you can find "daylight" bulbs at your local canadian tire, etc. that will fit the fixture, they should make you happier than your current setup. typical "daylight" bulbs range from 5000K to 7500K, with the lower numbers looking more yellow, and the higher numbers moving from greenish blue toward purplish/pink (9325K bulbs are often described as "pink" or "purple" when viewed against a flat white background) 10,000K bulbs are the most impressively "white" in my opinion, and to my eyes, seem to illuminate the tank more. if your goal is for the tank to "look" brigher, then those are the way to go. if your goal is for the plants to receive more light that plants can use in photosynthesis, then anything from 5000-10,000k should suffice, but those with specific phosphors (coating that gives bulbs their "color") for plant growth (full spectrum, plant & aquarium, gro-lux, etc) are specifically designed for their output in the photosynthetic range for most plants. red plants require more light (wattage, not color temperature) than green plants to keep their color and stay healthy.
choosing light bulbs is tricky, as everyone likes things to look a little different in their tank. I used to use strictly 10,000k and 6,700K lights in my 29g tank, and while it looked VERY BRIGHT and the plants grew well, after a few months, I got very tired of the glowing white box and thought that it looked a bit unnatural and switched to GE Plant & Aquarium bulbs. These have no listed color temperature, but put out light that's probably somewhere in the 8,000K range or the 4,000K range in "apparent color temperature" as it can look like a comination of purplish and orange. (most likely spikes in both of those regionsof output for these bulbs). My plants do just as well if not better with these bulbs, which are cheaper, and have a much more "mellow" appearance. here are a few links on color temperature, the theories behind it, and misuse of color temperature designations by bulb manufacturers:
I hope this helps. If your bulb is indeed 20w and not 30, you'll need to decide if you need a 20w t12 bulb, or an 18w t8 bulb (most ballasts these days can handle either, and all should be able to handle a t12. t8's are "newer", but have been around for quite some time now, and should be handled just fine by your ballast)