need help diagnosing my plant's problems: brown spots and yellowing

Aight so I have a few plants that are sick and I can't quite figure out what is going on.

I was thinking that it might be a nitrogen deficiency, but before I give them some I wanted to make sure.

I have 4 plants under a 90 watt led ufo light in my closet
the soil is a mixture of organic miracle grow soil (60%) and perlite (40%)
the temperature is around 75 degrees.

many of the leaves have brown spots
the new growth has brown tips
some of the leaves are yellow, and the bottom ones are very pale yellow

i would say check ph cuz of the rust lookin color. there does seem to be a lack of N but no point in adding if the ph is off. also i know u probly heard this before but miracle grow is a no no

dont automatically take my reply to heart as im still a newb

woooo can i get some +rep for my first right answer?

Thanks for the help guys! a couple more questions, so I decided to cut up a couple lemons and juice em then mixed it with water and waterred the plants, think that'll work?
I'm gonna buy some ph testers tomorrow.
If they still need some nitrogen, at what point do you think I could start adding some?

thanks again!

if u were gunna try to adjust ph without checkin it first the best course of action would have been to use dolomite lime. u could start adding now just start at 1/4-1/2 strength so u dont accidentally burn it.

Looks like nute lockout due to ph troubles. Lemon Juice will drop your ph even more. Check your PH first and see if you need to raise or lower it. Nutrients are mostly available in soil between PH 6.5 - 6.8. Hope it helps.

Bought a digital ph tester and some lime, the ph level is around 6.0 so I'm gonna try and raise it
Thanks for the help