Growing Lomandra longifolia (Dwarf Mat Rush)?

I have the problem of lack of chlorophyll in the top half of Lomandra longifolia leaves due to either a fungi or mites; I am unsure. They are in sun and sand on Bribie Island Qld. I watered with borewater, non-salty to the taste yet undrinkable. What can I do?

Hardiness Zone: 10b

By peter from Bribie Island, Qld, Australia