Adofix p II powder, can I use it a bit at a time?

I’m getting into developing my own b&w film and I aim to do it as cheaply as possible, without sacrificing the quality and durability of the negatives. Rn I’ve settled on rodinal (very diluted), no stop bath, adofix powder and maybe adoflo (I don’t want to risk it with dish soap).
Problem is, one bag of adofix can make 1 L of solution to develop about 10 rolls and only lasts about 6-8 weeks once mixed. I know I’m never going do go through 10 rolls in that amount of time, so I thought that, since I only need about 250-300 mLs of fixer per roll, I’m just going to weight out the grams of fixer I need to make that quantity and save the mixture after developing, so if I come back to developing within about 2 months I can use it again, if I don’t I will only have wasted a quarter of the bag.
Is this doable or will the powder go bad anyway once opened, even if I don’t mix it with water?