Need some help with yellowing leaves!

So this would be my first and hopefully last post. My plants are 2 weeks into veg stage. There are 17 total plants and about 7 of them have started to turn yellow. Same soil , same water in all. Ph of my water is 7. The plants are under 2 400 watt mh and I'm watering every 3 days. Temperature ranges from 70-85*. I have good air movement but no real fresh air coming in. I need as much heat as I can get without having to run the heater too much. Although there is about 15 feet of empty space where ouside air comes in.

f.e.e.d. m.e.. u make no mention of nutes. u have to be experiencing some significant growth under those lights. increased lighting=increased nutes-or start them if the case.
so u r saying there is high heat with little fresh air. add some co2 to the equation to balance them out. alos some fine dolomite lime added to the top layer of your soil will come in very handy after about 1-2 more weeks

Can you reccomend me some type of nutes to look at ? I was worried that since techniquely it was supposed to feed for 6-9 months that if I gave them extra nutrients it could be too much. Was I wrong to make this assumption ? I just started adding schultz 10-15-10 Plant Food Plus to the water. Opinions ? Also the first ten have been in about a week and a half longer. All have shown tremendous growth in the past week or two. As for the heat it never gets above 90 and never below70. Would it be best to look into a co2 system or put in some form of fresh air ventalation? Or both ?

fresh is easiest and best. co2 is useless unless you have eberything else nailed to the tee. as for nutes, fox farms is ok, canna is ok, stay away from GH as tends to be excessive salt buil ups. I think the soil is supposed to feed for 2-3 months tops.

ok so here is my plan of attack. I just purchased the fox farm nutrients , I'm currently putting in an inline fan to draw air from another area of the room. Although I don't want to get straight outside air because of the temp I think that any type of fresh air would be good compared to none. Thanks for the help bandit I'm sure I will be posting again soon!