container size

Should I add the volume of Excel ill be using (5ml), to the amount of distilled water ill be using (250ml) in container size for a more accurate analysis of my solution? Or is the addition of Excel not relevant?

Newbie here, but Ive been mixing my own fertz for awhile now. Unfortunately non of these batches have turned out well. I think my confusion is over the Container size field. Can anyone explain to me like im a 2year old as to why Rotala Butterfly bases calculations on container size rather than...