Yellowing of leaves please help!

Hey everyone, long time reader first time poster. I'm hoping someone can give us a of help here because I'm quite worried!

Okay, SO this is my second grow, I have 6 clones that are 3 weeks old under 1 x 600W MH bulb (converted from HPS ballast) in a closet grow. Potted in soil with around 20% perlite. The closet has good ventilation with an in and out fan running and it rarely gets up higher than 30 degrees C (86 F). It started off with one plant yellowing on a few lower leaves about 4 days ago. It has spread to 3 out of the 6 clones with the first one in the worse shape. now there are leaves at the top starting to yellow as well on the other plants and I'm starting to freak coz my babies are hurting!

The first plant is starting to have burns/ brown spots on the edges as well. I can't tell if it's nute burn or something else. I read around, and it's sounding as if the yellowing is a Nitrogen deficiency, so I've added miracle grow with 20% N in it, not sure if I may have over dosed as to that's because of the spotting or what. I'm afraid to add more MG in fear of worsening the problem.

Also, I have no idea what strain these plants are as they were just taken off my largest plant last grow from seeds I'd collected over the years. Would anyone happen to know the strain just by lookin'?


THANK YOU in advance!

yeah its a def bro like u think i do believe but give it a few days to add new leaves foliage and look at them but if the edges r browning up or yellowing its nute burn..

The yellowing from the bottom leaves up is absolutely classic nitrogen deficiency. The burning is either heat stress or a ph problem.

Ok great thanks!

I don't think it would be heat as the temp stays at the same temp and the burn is on the lower leaves mostly so prob nutes. To fight the N deficiency you reckon I should keep using the MG even though I might have nute burn?

The soil tends to dry out quite quickly, I've found myself watering it every couple of days so they don't dry out too much. ( haven't seen many signs of overwatering; drooping branches n such). Would the sulfur help with the N problem?

Cheers