A: This can be a tricky problem! In order to grow, mold loves a moist, dark, warm area. In most cases where I have seen this problem, the toilet tank water has been raised to lukewarm temperatures for some reason, which completes the triangle for the three things that may attract mold. Tank water can warm up due to the toilet tank being located directly over a heating source. Some toilet-water feed lines have hot-water mixer valves on the water supply to cut back sweating of the toilet tank. Either way, that could heat up your tank water. Check to make sure you don't have lukewarm water in your tank and address the problem if you do.

Also, if your toilet is broken and running constantly, it may account for extra moisture at the top of your tank. Check for that, as well.

Finally, you can purchase some good additives that may control tank mold. Be careful, though; some additives can shorten the life of the rubber parts in your tank.

I'm sure we'll get letters from a lot of people with this same problem, and if I hear a good solution to an oldie-moldy toilet tank, I'll be sure to pass it along.