I think its just before you add it.I take issue with the MB7 additive.
If you read the bottle on microbacter, It warns you about introducing anything not native into the bottle. It is also bacteria which needs light.
Pouring MB7 into a translucent container with additives is counter to their instructions, and just thinking about it, seems like you're going to be growing things inside your newly mixed container. That gives me the ugs
Not in the pre mix or adding to the tank around the same time.