Yellow leaf and brown spot

Hi guys I'm growing 4 plants 3 Lemon skunk and 1 moby dick , I'm using 600watts MHL temp btw 75-82 humidity 50-55% my plants are 2 weeks and 3 days old they almost 4" tall on the 4th set of leaf the problem is the bottom leaf r lime green or yellow and 1 plant has a brown spot on the leaf I don't know what is't or what to do , is my first time ever growing so please if any1 knows what is my problem get back to afaik don't want my girls to dying , I'm also using org soil and fox farm nuts just 1 a week and water when the soil is dry , I'm not able to post some pix so sorry about that , and I think for 2weeks and 3 days are growing very slow ..why? Thank u guys alot hope hear from 1 of u guys and help me out with this .... Peace
 
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