Are you using nutes yet? If so, you might just have a tiny bit of nute burn happening, or if your water ph is off you can end up with similar leaf blotching.
Out of curiosity, are you using a HPS light right now?
I am using nutes and ppm is around 600 and ph is 6.0 I have a 400 watt hps but not using yet until flowering maybe in two weeks.The plants are under flourescent lights 2 of them both around 23 watts and i think @ 2600 lumens each bulb