Help yellowish green plant sum brown spots

i have a couple plants that starting to fold up,few dead spots and brown tips and small brown spots i have a couple plants that starting to fold up and brown tips and small brown spots & 1 of em turning yellowish green...there 15 days old...temp is 78....i water every 2 days...gud airflow.. and i use only mircale grow potting mix n the cups...my buddy says thats the problem using only that mircale grow potting mix is starting burning the plants....another says cause i use 24 hr lights... the lights aernt close..bout foot off..and yes i use tap...please let me know sum thing thanks

Have a look at the pictures I attached ... is it like that?

I have a number of plants, all healthy, bars this one particular plant. The nutes/medium/lights for the rest of my plants are exactly the same for this one - so not sure why this one has turned sickly. I'm on the verge of pulling this one.

miricle grow is a hot soil. so sometimes it can be rough on the wee ones. best advise I can give you is dont use any nutes for one. and when you water let it run off a fair amount each time. last do not overwater, let the plant start to wilt befor each watering... these are the basics, but if you follow these few simple rules they should be ok