Brown spots on leaves DWC

Hello, this is my first grow and i have 2 plants and they are 17 days old. one of them seems fine but grows slowly and one of them grows fast, it seems fine except 2 fan leaves.
my light 400w DIY dob led, and i use general hydro flora series. im not planning to have best grow results, just want to smoke my own product

bubblegum kush auto

light schedule: 6on 2off

ph around 5,7-6.00
ppm 700
heats: 20-25 degrees C
water heat:18-22 degrees C
20lt bucket using 15lt, indoor grow.


im thinking this is a calcium problem but im not sure, i use call mag today. i need your opinions. what u guys thinking?

What is with your light schedule?!? I imagine all that is doing is confusing the hell out of them. If those are autos they can handle 18+hours of light, some strains can handle a 0 dark schedule. I guess technically your are giving them 18 and 6, I just never considered breaking it up. Anyway, I agree, calcium, but they do seem a bit young to need it. It could have just been sprouting damage.

hey @Johiem thanks for the comment, i read many things about 6on 2off light schedule for autos and its make sense to me, plants can use light for 7 hour this is the main idea for this schedule. after that they can rest and after 2 hours they can start working again. this is my first grow and i want to try something new lol. yeah i hope its calcium nothing else. i give them 20ml gh cal mag today. lets see

im just scared about root problem or something like that

If the roots are not brown and slimy, you're good.
Based on the pics it does appear to be the start of a Ca def., but it may have been some stress the plant had while establishing its root system in the bucket.

@GBAUTO thanks for the comment mate, roots seems fine to me , i dont think she has any stress or something like that. i hope its ca def