At just about any store that sells swamp cooler parts, you should find
"algae blocks". I can think of one called the Fresh Air Block. These are
simply placed in the pan, under the inlet water flow, and allowed to
disolve. You might have to check on them monthly depending on your cooler
To learn more service and repair information on evaporative coolers, visit:
The Cooler Doctor
Service, Repair & Enhance the Performance of Your Cooler Yourself and Save
$100s Every Year!