Brown/Yellow Spots on Plant

Hey guys, I just joined the forum to look for help on my first grow. The past few days I have noticed some spots forming on my leaves that are freaking me out. I have a 150w HPS flowering 3 plants. I got these chemdawg clones and vegged them for a couple weeks and just switched them over to 12/12. During my veg period I didn't give them any nutes, i was told to be very careful with giving them nutrients. I ordered the fox farm 3 package (big bloom, tiger bloom, and grow big) and I am supposed to get them by tuesday. I am worried that they are starving for nutrients but I'm not sure. As soon as i get the nutrients i plan on giving them tiger bloom and big bloom according to the fox farm chart. Any idea on these spots on the leaves? I noticed in the past week the leaves have also gotten lighter green compared to the darker green they
were. Any help and advice I would appreciate. Thanks alot!

GET sOME Ca Mg

I put about a 1/4 of a teaspoon of epsom salts in a litre of water and watered the plants with it. I also put some in a spray bottle and misted the leaves. I guess we will see what happens.

The plants bounced right back. I put some Fox Farm tiger bloom and big bloom and they look better than they ever did and have exploded. They are in their 3rd week of flowering. Plants are about 4 feet tall with the 3 gal bucket. Strain is chemdawg, any idea on how long of a flowering period i am looking at? Thanks for all the help.

Edit: I also forgot to add i switched to a 600w HPS air cooled by a 6" Inline Fan and they are in a 4x4 tent.