Yellowing leaves! HELP?!

[meandean]

Well, Hello to all fellow growers! My problem is that my leaves are turning yellow. As you can see by the pic., it's green in the viens, but yellowing all around. Which nutrient are they not getting enough of? They are about 3 months old and are growing at about 1.5 inche's to 2 a day. The one on your left is of a sativa and the other is of an Indica Strain. Please HELP ASAP. I just started Flowering stage and I want to nip this in the Bud, before it's a problem. Thanks, and smoke another one.

[Farmweed]

post as much detail as possible: what they're being grown in? what light source you using? what your feeding them with and how much? etc

im on my first grow but others here can help.
goodluck

[meandean]

They are in shultz potting soil, using 400 watts of Florucent lighting. Custom blend of Fert. 24-8-16, during veg. stage. Just gave them new fert. 18-24-16. Hope this helps alittle.