Problem 5 week in flowering

Hey all,
I'm having a bit of a problem with one of my plants... Quite a few leaves have been dying recently + i'm seeing rust spots all over the plant.
I've now been flowering for 5 weeks +2 days out of 10 weeks.
I'm growing in soil and re potted in some very rich soil at the beginning of flower. I've only been feeding 1/4 recommended dosage of tomorite&seaweed ext (20ml per 4.5L) once a week for the past 2 weeks.
This is the plant in question:


And problems with some leaves i'm pulling off:



Thanks for any feed back guys, this is my first grow, so i'm not quite sure what to expect from see these plants to the end.
Cheers,
T

Personally I would relax. It is normal for plants to feed off their leaves in the last stages of flowering. There is absolutely nothing wrong with your plant.

My guess is #4

Nutrient Problem Solver Chart

This handy chart is a guide to determining the possible problems with your marijuana plants when it comes to fertilizer problems. Diagnose the problem very carefully. Do not make major changes to your plants feeding schedule. Instead slowly correct the problem to determine if diagnosis is correct.
Start Here
1a) The problem only affects the bottom and middle of the marijuana plant. Go to #2.
1b) The problem is affecting the upper top of the marijuana plant and leaf tips. Go to #10
1c) The problem is affecting the whole marijuana plant. Go to #6
2) Marijuana leaves at the bottom and middle of the plant are drooping, yellowing, then dieing. Leaf are not curled up. Vegetative growth is very slow. Possible problem is lack of Nitrogen. If not go to #3.
3) Some leaves are curled up or worst twisted oddly. Leaf is yellowing (and maybe turning brown), but the veins remain somewhat healthy green. Possible problem Magnesium. If not go to #4.
4) Brown dead patches around the edges of some of the leaf, which may also be curled. Marijuana plant may be growing too tall. With big gaps between brackets. Possible problem Potassium (K) deficiency. If not go to #5.
5) Leaves and stem are dark green or red/purple. Leaf falling off plant. Growth is slowed and leaves are small. Possibly problem Phosphorous (P) deficiency. If not go to #6.
Signs of Too Much Fertilizer
6) Marijuana plant looks healthy, but leaves are turning yellow, brown then falling off. Possible problem too much fertilizers, over-watering, or insufficient soil aeration. Cutback on fertilizer feeding. Flush marijuana plant with clean water. Check to see if roots are damaged or become a ball. Drive a stake around the edge to create air flow. If not go to #7.
7) Leaves are curled under like a ram's horn, and are dark green, gray, brown, or gold. Possible problem over-fertilization. If not, go to #8.
The plant is wilted, even though the soil is moist. Possible problem over-fertilization, burned roots from too much fertilizer, root bound, marijuana plant disease. If not go to #9.
9) Marijuana plants won't flower, even though they get 12 hours of darkness for over 2 weeks. Possible problem is light leaking into the grow room. Too much nitrogen, pruning or cloning. If not, go to #10
10) Leaves at top of marijuana plant twist turn brown then die. The lights are too close to the plant.

Cheers for the input guys. I think you're right with 4, tho 5 and 2 sound about right too. It's probably down to underfeeding.... I'll go to full strength on nutes tomorrow. Cheers boys