brown marks on leaves

Hi has anybody got any idea what the marks are on my leaves, its not the ph i don't think its nute burn or to close to the light, i had nutrient burn and that sorted now i had nitrogen problems aswell but they are sorted my lights are 2 300w and 4 35w but they aren't to close either, my growing medium coco fibre and clay pellets and fertilizer is canna A and B and my plants are 8 weeks old tomorrow they have been in flower for 2 days now but they have had the brown marks for a few weeks thanks

i cant upload any pictures at the minute for some reason but i will get them uploaded