Don't know what it would be or how it would work, but several years ago a place I worked finally splurged and bought 2 big new evaporative coolers for the plant.
I wanted to get the most life from them, so I did some research.
Turns out they are very efficient at collecting solids (salt) in the water, which is highly corrosive to metals.
Like the Dead Sea, water comes in, but doesn't go out other than evaporation. That leaves all the minerals behind!
What I did was coat the inside of the pan and up the sides, the tops of the drip trays with coal tar epoxy. Did that when new before everything got crusted with deposits.
Then set up a small valve and drain connected to the pump so anytime the pump was running a small amount of water went to drain. That kept the salt build up down.
Then connected a 6"x6" square of sacrificial aluminum to a heavy copper wire, grounded it to the frame, supported it on a piece of rubber below the water level in the pan. Once a year the aluminum would have to be replaced as it was eaten away. That meant it was doing it's job of protecting the rest of the metal.
It must have worked, they still looked like new inside after about 10 years! Who knows what happened after I left, I doubt they were maintained after that...