Matt,
Try 2 or 3 drops(5.25% - reg Clorox) per 10 gal. I think that will provide
the protection you are looking for. Should keep forever in a closed
container without overdoing the Cl. Will try to do a test and update in a
day or so.
Jim

"Matthew Donadio" wrote in message
...
Hi all,

I just got a 10 gallon water cooler to store water in. The cooler is
totally opaque (it's one of the yellow Igloo pigs), but I'm thinking that
I
should add something to prevent Icky Stuff from growing in it. I have
Physan, but that's a bit expensive to be constantly using. Is household
bleach OK? How much per gallon?

Thanks.

--Matt