Yeah i agree with daihashi, it does look like a little bit of nute burn. Personally I like to flush my plants roughly every month, i use organic ferts and i've been told that you don't need to flush with organics but i don't think a flush can do any harm. Just something to maybe keep in mind should the problem get worse.

I use bio bizz grow and bio bizz bloom. For vegging i just use the grow and in flowering I use both the grow and bloom combined. I start with 1ml per litre between 14 and 21 days old, go to 2ml per litre weeks 3-6. When i switch to 12/12 I back off on the grow to 1ml and start with 1 ml bloom also, I keep the grow at 1ml thoughout flowering and increase the bloom gradually to 3ml by around week 5. I'm no expert but thats how I do it. But i'd change it around a bit to suit how big the plants are and how long i'm vegging etc