MIX soils?

hi i have a noob question i have 5 plants growing right now 3 of which ima keep for mothers........so here it is......is it safe for me to mix the soil im using right now for them(pro mix) with soil i have laying around ( ff ocean forest) thanks help would be appreciated because i plan to swich them from 3 gallon containers to 10 gallon in about a week.

I do it all the time. I have plants in like 5 different types of soils.

from what ive heard ffof is really good so id say so.