1st grow mid week 3 can anyone help ?

I just looked up your light (as per your grow diary) and it's similar to the V600 model which I have used in the past. I doubt it was that which caused the issue. So I don't know - you can see that it's affecting multiple leaves so I'm not sure that its water damage, hence my suggesting you re-check the peak temperature and humidity readings. Other than that your plants look pretty healthy to me so if it doesn't spread I wouldn't worry too much. Good luck!

If I had to guess from the photos alone I would say minor heat or humidity issues - are you confident on the figures you gave? Do you have a min-max view on the hygrometer/thermometer? You said yourself that you only fed a 1/4 nutrient strength, so it shouldn't be nute burn, and you said your PH is 6.5 which would be correct for soil. I'm looking at your diary photos... are you using a UV light? In particular, a UVB light? If you are, you might be burning the plants as they have to be used in moderation. Even UVA needs to be increased gradually.

no non è una bruciatura da nutrimenti perche sarebbe su tutte le foglie magari è rimasta dell'acqua sotto alla luce e le ha bruciate se guardi le foglie hanno un bel verde che arriva sulle punte quindi continua e non preoccuparti ..