My leaves are getting brown spots and drying up.

I just took these leaves off my plant to take a picture, but a lot of my leaves are doing this. I am in week 4 going on week 5 sence I put them on 12 and 12. What could cause this to happen to my leaves. The leaves are dry, curling, and the ones that aren't dry all the way, have brown spots.

Your experiencing a nutrient deficiency! Have you changed to a bloom nute? you need high Phosphorus (however its spelt). Hope this helps. let us know if your already using a bloom nute!

It might be a nute lock up! Flush it and renute it!

I think it could be P (phosphorus) deficiency also as 'grow4me' has suggested.
P def' will look like that and the leaves get real twist to them on the ends.
Also, brown rust spot could also mean calcium def' so I'd be running some cal/mag as well with your feeding.
During flowering you need high P but also you need plenty of K (potassium).
What nutes are you using?

I've been using Sugar Peak (hydro organics) Flowering. But I ran out and wasn't able to feed them a few days over their regular feed time. could that be it? Yesterday I bought Fox Farm Big Bloom and Tiger Bloom and fed them. Will that shit cure up now you think? Should I pic off the rest of the leaves that have that on them?

Brand is only as good as NPK breakdown. FF has a pretty good rep but I've never used them.
What's the NPK?
Leaves that are are around 60 - 70% pull.
No reason the plant should be trying to repare them.
In saying that don't strip a plant if they're all f*cked, leave the best of the worst if it's that bad.
Plants still need leaves to live
Remember this is a weed and just needs a reasonable environment and good all round ferts.

Sounds like a phos def so i would flush the plants with a ph of 5.5 and see if your local nutrient dealer sells anything that can add that little added phos to the nutrients that you allready have.It may just be a salt build up you can never tell i would flush the plants with a load of just plain old water from the tap ph it and flush.Do this in the bath if possible then once you have flushed leave for a hour so that the excess water will run off then make up a new batch of nutrients and give them a feed after a hour of the flush then give them a extra couple of hours to get all the excess water out and see how they fair.And no all that water won't hurt the plants [Read your mind see].