I see that Superthrive is basically seaweed extract and there is plenty of controversy about it's effectiveness as a fertiliser. Down here Seaweed extract cannot be sold as fertiliser as it has variable amounts of nutrient depending on the source of the seaweed, processing and time of year. 7.9.5 is also very low N which is the element that contributes most to green leaves.
All your other factors sound good. maybe try an alternative fertiliser for a while. Preferably one with real nutrient.
Stress is none major factor that causes leaf drop - Too dry, too wet, too cold, too how, not enough sun, etc. Another factor that causes leaf drop is natural old age. Individual leaves have a finite lifespan of 1-3 years. Older leaves are lower on the stems because they opened first. If only lower leaves have fallen maybe that's a possible cause?
Directions that state every other day are only very general guidelines. Does not allow for local conditions, time of year, temperature, wind, etc, etc. Relying on calendar to water will only cause problems. Definitely water according to soil moisture. Check with a finger or keep a stick in the soil to check soil moisture. If soil is damp on second day (or third) do not water! Only water when the soil gets close to dry. At some times of year your tree might go for a week without additional water. Other times you may need to water every day or sometimes even more. Most Ficus sp are quite happy to have a dry period between wet. Constantly wet soil definitely causes problems with root rot and probably responsible for most indoor plant deaths. That's why I mentioned the tray but you seem to already know not to let the pot sit in water. Now need to water only when soil requires more water.