Hey Kushmun you can do that or the route I would probably go because you have promix you can up pot using that and feed some other nutes untill MC is available and just switch nutes when you can.
420 Magazine
oldsmokey
Virgin Ground
MC is available in 22# bags. It is the only size being offered at the moment.
It is the newest version that they are shipping out right now.
Save 6% with the code MegaCrop.
It is the newest version that they are shipping out right now.
Save 6% with the code MegaCrop.
oldsmokey
I tried the free sample by the time I used that I was convinced enough that I ordered the 10 kg bag and I'm only growing 4 plants at a time. So I have enough probably for several years but it is cheap works well and easy to use. There is quite a few people on this site using it with good results. My first grow with megacrop yielded 2lbs 12 oz from 4 plants and I did make a few mistakes along the way. So it's your call but that's a lot of mega crop for one plant.
oldsmokey
You could try emailing greenleif and ask when smaller sizes will be available.