Preventing mold in humidifier tank?

Have a furnace mounted humidifier that works with a media mounted in a wheel that turns in a container of water. Sears brand. The water is city water. Does anyone know of an additive that is safe to use and effective at preventing mold in this situation? The water continuously feeds in as it evaporates, but there is not enough change to prevent mold from starting within 2-3 weeks of thorough cleaning.
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Have a furnace mounted humidifier that works with a media mounted in a wheel that turns in a container of water. Sears brand. The water is city water. Does anyone know of an additive that is safe to use and effective at preventing mold in this situation? The water continuously feeds in as it evaporates, but there is not enough change to prevent mold from starting within 2-3 weeks of thorough cleaning.
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We add about 1/4 oz of Clorox to the water in the container every month or two , just enough so that we don't get chlorine odor in the house. Very effective, and there's no sign of damage to the unit after 30 years of doing this.
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Stoney writes:

Swimming pool polyquat algaecide.
It's the same type of "anti-bacterial" ingredient as in so-called "anti- bacterial" hand soap.
By the way, which is only "anti-bacterial" in the sense that the polyquat keeps bacteria from growing *in the soap itself*. The marketing dept hopes you'll assume that it somehow keeps your hands free of bacteria more than ordinary soap, which it won't.
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I'm guessing that it's a drum type humidifier.
If it is, except for flushing the pan regularly, there's really nothing you can do with it. Any chemicals you put into the pan will end up in the air stream.
I'd replace it with a bypass humidifier.

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Just about any hardware store (sears included) will sell tablets that you drop in for that purpose

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IK haven't tried this but i'd guess that a strip of zinc in the water would retard fungus. The zinc salts produced won't evaporate so there is no risk that they will get into the air stream.
RB
Stoney wrote:

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