2 Week old lower leaf brown spots

Hey i have been looking at this website for sometime now and i am very new at this. My first babies die pretty fast because i did not let the roots grow very far out of the rockwool. Now on my second try they look much better but starting to have issues again.

Here is my set up
PH always at 6-7
using a 90 watt fluorescent for first plant
using a 18 watt/120 watt for second plant
both lights 1 1/2 from plants
soil is fox farm ocean forest
used rockwool for 1 week sprouts then planted rockwool into soil
temperature is a little low 65-75 but i am poor so i cant get a heater
full closet size box outline with aluminum with fan sucking air through
all in a dark unused closet

K so you know my set up now the issue. I am doing the exact same thing to all my plants water light etc....2 of them seem to be doing fine just a little limp but on one of second plants there are small brown marks on the lower leaf but only on one of them. I have not started to feed it nuts. cause i was told that ocean forest supports it food wise till vegetation. If anyone can throw me some tips lemme know. Here are some pictures. the last one is the one im having issues with

any help at all would be nice

Probably burned the leaves bro. Maybe bring the lights up a bit?

ya i moved the up another inch so there at 2 1/2 inches but i mean there only 90 watt fluorescences..i was told you can keep them an inch from the plant......someone did tell me that since i made the mistake of misting them with a spray bottle under the light it caused the burn but we still havent figured it out....ty for the input tho

sucks im not getting much help from anyone...ples if you have any input lemme know because the brown spot is on both sides now...both bottom right and left nods are spoting brown....

Late but those yellow bottom leafs arent true leafs and will fall off no matter what.

the cotyledons are brown because you are overwatering it, or could be nute burn from the soil?

but i mean, that exact thing happened to me about a week ago. plants look exactly the same. i was overwatering it.

but i have no exp. with rock wool..