The 1L powder kit cannot be mixed in parts. You can just use 500mL or 250mL at a time instead of pouring it back but it doesn't really extend the life of it. I had a bunch to do so yes, I just poured back what I used each time.
Originally Posted by SMBooth
I've started adding 30s or so to the time so 4:00 dev and 7:00 blix. The blix is oxidizing so I'm not sure how much longer it will last but I'm already past the advertised capacity. I would still like to get another 3-6 rolls out of it if I can. I have another 3 rolls of Portra 160NC 120 and 3 of Superia 800 135-24.