Lower leaves yellowing

I was hoping someone could give me some advice. I'm growing Passion#1 indoors they are 6 weeks old. In the last couple of weeks the lower leaves have started to go yellow between the veins and then spread outwards until eventually the leaf just falls off.This is happening to new & old leaves but only at the bottom of the plant so far. I was checking for defs but they mostly say if its the lower leaves its the older ones. Sorry I don't have pics but if you have any ideas Please let me know.
Thanks in advance.

at six weeks you need to start feeding if you haven't already sound like you need to read the faq again check in the links theres some very helpful stuff some of it you may need to read twice if I had to guess maganeese def happen alot during veg check your soil PH more info would be helpful temps ect

Thats the thing I've read it, I have the bible and none of them describe this. I'm using BioGrow 1ml to the litre. The leaves are sort of blotchy also. Other than that the plants are healthy about 3feet tall so I'm going to put them into flower in the next week.

Phily Kelly said:

Thats the thing I've read it, I have the bible and none of them describe this. I'm using BioGrow 1ml to the litre. The leaves are sort of blotchy also. Other than that the plants are healthy about 3feet tall so I'm going to put them into flower in the next week.

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Phily Kelly,
Do you have some pics?
Are the leaves curling upwards? Do they have brown splotches on them?
From what you're describing it sounds like a mag deficiency.
I know in many of my posts on this particular section I say this, but from the pics I've seen of other's plants and from my own grow troubles, it sounds like a mag def.
From more experienced growers I've talked with on other forums, a mag deficiency is a common problem with growing weed. It is also one of the many minerals that is easily overlooked. A magnesium deficiency can cause nute lockout. Magnesium is a necessary mineral for clorophyl production.
I have rarely seen any organic or non-organic ferts that have magnesium, and the ones that do have a very very small amount.
The cheap easy solution is to mix a tbls of epsom salt/gallon of water (make sure the epsom salt is completely dissolved before applying). Put some of this mixture in a spray bottle and foilar feed for a few weeks. Unfortunately the affected leaves will not repair themselves, but it will keep other leaves from doing this same thing.

Here's a good website I've found that has pictures of all kinds of plant problems.

Grow Marijuana FAQ, Cannabis cultivation - marijuana growing tips & photos

good luck!