How to de calcify a pot without using chemicals.?

Yes. Vinegar removes lime scale (calcification). Just boil the vinegar and then lightly scrub with a plastic scrubber. You won't have to scrub much. The vinegar does a great job. I wouldn't dilute the vinegar, tho. Just use it right from the bottle.

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If it's nonstick (teflon), that's worth a try.

If it's cast iron or any other material, a paste of coarse salt and oil is best.

I've seen ice and salt used.Fill it with ice and salt and swish it around.