watering and fertilizing paphs

[Pokey49]

My orchids are in our sun room. which offers plenty of light but not direct bright light this time of year as its on the north side of the house. The orchids sit along the north wall. I keep the sunroom between 60 degrees at night and 70 at day. I am fertilizing 1/2 strength with the ratio noted above 1x per week and flushing to get the salts out every 4th-5th week with plain water that is luke warm. My other orchids (Phals, cyms and epidendrum) look fine. Its this one paph that the lower leaves are looking poorly and I dont want to duplicate on the 5 new one sI have, whatever is going one