Perhaps someone can make a suggestion.
I bought a new evaporative cooler last spring. (An evaporative cooler replaces an A/C in dry weather and costs much less to run. It runs water though pads, which have air sucked through them and blown into the building. They work quit well.)
This spring, as usual, I prepared it for a summer's use. Replaced pads, lubricated blower, cleaned the interior, and checked it out. For the first time I found a inch or more coat of calcium from my hard-water well in the bottom of the reservoir (about 3 x 3'). Never happened before in some 30 previous years. Granular on top and a 1/4 to 1/2" of solid below. The problem is removing the solid. Scraping will take many many hours and will surely damage the paint. I'm currently trying a generous amount of Lime-a-way (active ingedient unlisted) in an inch or so of water on it. Helps, after a couple of days, but not very much. I tried adding some toilet bowl cleaner (20% hydrochloric acid) earlier this morning but so far little help. I don't want to damage the baked-on enamel paint if I can help it. Swimming pool acid sounds rather drastic to me.
A cooler book I have suggests a tile and tub cleaner. Those I looked at at Walmart didn't say much if anything about removing calcium so I will use the TB cleaner instead - this brand (The Works) works VERY well on my toilet the past few years.
Evidently my well water has suddenly this past year become much much 'harder'.
I have plans for avoiding this problem in the future but first I need to remove what's there now.
TIA