Abnormal mottling on Paph. Druid Spring

[CMW]

They are under florescent tubes, 3' long. One 'warm white' and one 'cool white.' The tops of the plants are about 12" away from the lights. Right now they are getting 12 hours of light, and the time will be increased a bit come spring.

I am using the MSU fertilizer, R/O water formula (and I water with R/O water I get in 5 gallon refills from the grocery). I fertilize once every other watering, at about half strength. Less often in winter, of course.