Yellowing Leaves Nute Burn Or Sun Burn ?????

Ok im a first time grower im trying to grow 3 plants i dont know the strain im growing with sun light during the day (I live in spain so its pretty god sun) and a 150 watt bulb for a few hours at night
I have them on 18/6 and im using Masso Garden abono universal i asked the guy in the shop and he sid that it would do untill they get bigger but ive been feeding with mainly water cos the soil is new and already has nutes in it i think :/
the temp is around 65-80 degrees and i have 2 different pot sizes the one with burnt leaves is 2.5L and i feed it 250ml of water andif i use nutes i use a quarter cap which is what it says in the bottle
Tomorrow im buying a 230watt 6500k bulb

If im doing anything wrong please tell me but remember i live in spain and cant get the propper nutes that ive read that most people use and im quite strapped for cash so any money saving tips anyone has would be really usefull :)

"andif i use nutes i use a quarter cap which is what it says in the bottle"

Those kids are burnt.
It is much too early to even think about nutes.

Wait for the 3rd set of real leaves.
When the new growth begins to pale, and and the cotyledons shrivel
Then start with 1/4 cap full every other watering.
Those tiny round leaves, (cotyledons), are all the food they need as sprouts.
Do not water them until they actually need water.

Lift the pot daily.
It's weight will tell you when it's dry enough.

Cannabis is a hardy weed.
It usually take too much love, or total neglect, to kill it.
Between those extremes it's easy to grow.

Aloha,

Weezard

Thanks alot ive been pulling my hair out wondering what to do
ive read so many different things but they were all about older plants so its good to hear something about my plant directly :)