looks like the start of nute burn...it is ok to feed jus not that fert yet...its for flowering as its low in nitro....would get alaskan fish fert 5-1-1...feed every third water at 1 tsp per gal
dude the stem turning purple is not a bad thing it is from the nutes and its fine i use a few diff nutes on diff setups and mostly the stems turn purple after giving my clones the second part of my nute stage and its deff not too early man you can give half strength nutes just after it poppes up for one week then go full strength veg form from and have excellent resluts