One of my plants has started to get brown tinges on the edges and I'm wondering why this could occur? I use liquid plant fertiliser so I'm not exactly sure which nutrient it could possibly be lacking. But my guess is maybe I leave the light on too long? I read that you should leave it like 8 hours or something but I tend to turn it on when I get up then when I go to bed I turn it off so it ends up being on for like 12+ hours. But the light is only 3 watts LED anyway, not really for plant growing. What do you think?