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.

My boy can't finish the whole tin wihin a month too. What i did is to transfer an amount into a air-tight container for daily use and keep the rest in it tin. In this case, the milk powder will not be expose to the air and hence, can last a bit longer.