For FM do you discard it one month upon opening? Or ok to give some allowance? I store the tin in Ziplock bag upon opening. Currently feeding BM and FM and it always takes more than a month to finish one tin.

Practicality, how many of us are able to keep up with all the parenting 101 golden rule? Personally i do not store the tin in a ziplock bag. I ensure each time after i open the tin, take what i need and keep it close immediately. As long as the milk has not harden i still use it.