For the last 2 batches of beer I've used a swamp cooler to cool off the plastic bucket fermenter. The cooling worked well, but on both batches, there was a bit of mold growing on the outside and/or under the rim of the bucket where the wet towel was. I added some sanitizer to the water in the last batch, but it didn't seem to help. Adding bleach to the water seems like a bad idea. Would there be any chance of bleach or another mold-killer ruining my bucket and/or beer from the outside? Is there something safe I can add to the water to keep the mold and other nasties at bay?
I've used bleach before without any problems. I can't imagine it seeping through the bucket into the beer, unless you use 100% bleach instead of water...
The amount of bleach required to sanitize water is something ridiculously low, so if its freaking you out, then just make sure you only use a little at a time.
"Most emergency experts and health officials suggest a mixture of 8 drops of bleach to a gallon of generally clear water for best results." - http://www.csgnetwork.com/h2oemergencypurifycalc.html
I'd suggest adding a few ounces of bleach every 2-3 days, rather than throwing in a quart the 1st day and leaving it, as it doesn't take much bleach to purify the water, but bleach does evaporate out of the water within a day or so.
There are professional additives that are used in labs to keep mold from growing in water baths and humidity pans inside incubators. Do you know anyone who works in a lab? Can you find a lab supply store in your area (there is almost always one to supply schools and child care facilities with science equipment). I don't know what the chemical is, I'll try to figure it out next time I see a bottle.
Bleach will work to reduce growth in the water, but it will not "combat" the mold that has already grown. You'll need to scrub and sanitize any areas where you can visually see mold, otherwise it will simply grow back in the same area.