Need help, first crop not so good.

I'm not sure what was wrong but any help would be great. Plants were in veg for 4 weeks and about 10-12in tall. They went for 8 weeks in flowering. The light used was 600watts and it was kept 14-18in away. The yield was very small and the buds were airy. Some of the plants yield was 3-4oz but others was 1oz. The strand is purps. I have include a pic of a couple buds and the nutrients i used. Thanks in advance.

http://i25.photobucket.com/albums/c67/turbo1k/stuff.jpg
http://i25.photobucket.com/albums/c6...o1k/stuff2.jpg
http://i25.photobucket.com/albums/c6...o1k/stuff3.jpg
http://i25.photobucket.com/albums/c6...o1k/stuff4.jpg