Yea I agree, I doubt that’s the problem.I did use this:
https://www.amazon.com/gp/product/B079KPHC5G/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
But only occasionally.
I'd be really surprised if it was the problem since it is for this use.
I’d try to do an ATI ICP test to check your tank and RO water to make sure it’s not entering through top up water or water changes.