I haven't a hard and fast rule. I'm always experimenting, and very careful about identifying the plants that are salt intolerant. I've scorched several with fert burn.
Time release fert provides some nourishment when I get behind on regular fertilizing with Growmore fert. Seaweed extract contains lots of interesting nutrients and some growth hormones. I've lightened up on the Superthrive, after reading some question as to how beneficial it is to orchids. Epsom salts for Ca and Mg lightly once every month or two.
And for some of my Paphs from limestone cliff habitats, I'll add a bit of dolomite lime every 4-6 months.