Rusty Spots On My Leaves

at the moment im growing a sativa strain, either thai or jamaican. its growing damn fast and im using organic fertilizer.
My problem is that on the lower to middle leaves there are yellow to gold rusty spots on the leaves.
I have heard of this problem before and have forgotten how to deal with it.
The plant is about a week and a hlaf old with four fully developed nodes.
Can anyone help?
thanks

it could be that your nute burning your plant... just if i were you run strictly staright water to your plant for about 2 weeks and see if it starts lookin better.. if it is nute burn that helps wash some of the nute out of roots... but it maybe pH levels in your water i've heard ideal pH level should be about 6.5..