Humidity tray: disinfectants?

[boytjie]

Hello all! Just wondering what others do to keep down the "grunge" factor in their humidity trays...? I've got the two-inch-deep trays under grids. The water gets filthy, and I'm starting to wonder if it could even be a breeding ground for pests, aside from bacteria. I drain and scrub them once a month (a job in itself), but what do folks do in between? Would a few drops of bleach in the water possibly help? As the bleach water evaporates, though, would the bleach harm the plants? Hmmm.