The bag says Sunshine Mix #4 is coco coir so absolutely not on lowering your PH to 5.5 or they will get more jaundice. I keep my PH at 6.0 -6.2 and it works for me, so go a little lower and some a little higher. The healthier the roots the less PH matters but its best to dial it in, 

Is your media drying out? Over watering and underwatering will both cause the leaves to look droopy like they do in the back. Coco coir is hydro so keeping it wet is important, my coco grows get watered 3 times a day and over watering coco is almost impossible.

Coco/Hydro also needs more cal/mag than soil