Q.My epiphyte is not doing well
We have had this for about 4 years now. We water it (mist) a number of times a week, have tried using fertilized water (an not fertilized), does not seem to make much difference.
It is in our sun-room, where it gets lots (8+hours) of indirect sunlight. Not sure what to do for it…

What kind of epiphyte is this? Since you have switched up your watering and fertilizing habits without success, I would suggest you consider a change of venue for the plant. I would try moving the plant in moderate light in the bathroom where it can get water from shower steam and see if it perks up.
For more information on the care of epiphytes, please visit the following link:
https://www.gardeningknowhow.com/houseplants/epiphytes/adaptations-of-epiphytes.htm