leaves turning yellow and dying at the bottom of my plants

hi i started growing 6 plants 3 of them where white widow seeds 3 of them were bag seeds they are in 2 gallon plactic containers with wholes in the bottom i got from work and i have been using nuts from this site http://www.formulaflora.com/ they are under a 600 watt hps light and are in my loft they have an extractor fan on them and a fan 1 dident grow and 1 was male so i am left with 4 plants all around 3 foot into there 3rd week of flowering and i have noticed that some of the leaves at the bottom of the plants are starting to go yellow curl up and die and there were some weird spots on one of the leaves here are some pictures if anyone could tell wat this might be would help alot thx.


https://www.rollitup.org/members/smokethebong-albums-my-ladies-picture43966-my-ladies-024.jpg

https://www.rollitup.org/members/smokethebong-albums-my-ladies-picture43964-my-ladies-015.jpg

https://www.rollitup.org/members/smokethebong-albums-my-ladies-picture45081-my-ladies-028.jpg

https://www.rollitup.org/members/smokethebong-albums-my-ladies-picture45083-img-0236.jpg

https://www.rollitup.org/members/smokethebong-albums-my-ladies-picture45082-my-ladies-019.jpg

not sure if i put the pictures on right

its ok..its normal..leaves at the bottom get less light.

looks like shes got a phosphorus def. those brittle brownish yellow spots on the leaves are a sure sign. if you havent flushed at all it may be a good time. and drop her some good flowering nuts, high in phosphorus.