On Thu, 27 Mar 2014 09:31:41 -0700 (PDT), jamesgang
wrote:

A filter will not change the water hardness. The water hardness is dissolved minerals, not trappable by a filter except an osmosis filter. They are individual molecules. Almost always calcium and magnesium but sometimes there can be a silica component. It's important to test for both. A conventional water softener can exchange the calcium and magnesium for sodium but will not do anything about the silica. The sodium dissolves much easier than calcium so it tends to not accumulate on home fixtures and in appliances. Since a swamp cooler evaporates the water there will still be residue, just it will be sodium instead of calcium. But it will be a lot easier to clean off. If you could set up your swamp cooler to occasionally overflow the pan then the dissolved minerals would wash out occasionally. That's how commercial ice makers deal with the problem.

Good catch. I was kind of thinking a 5 micron carbon filter. It would
be cost prohibitive to put a water softener on a swamp cooler. IMHO

Thanks.