are you using tap-water or RO water? I've seen similar in my Plagron-royal mix grown Hindu Kush when i used RO water without calmag.. ever since the prefertilization ran out and i started feeding manually (with calmag, because i use RO water) i haven't seen these marks anymore.. i asked at Plagron if calmag should be added to the water when using RO water when using royal mix, or if it already contains calcium and magnesium and i was told that i should add a little bit with RO water..