i just trimmed off about 20 dead leaves so they look scrawny

http://img520.imageshack.us/img520/9907/dscf2424ec2.jpg

i started them in april. i could be completely wrong and not giving them enough as i am very inexpierenced i noticed last time i changed the water about a week and a half ago i cut the nuits back pretty hard 7tbs and the yellowing began again after the previos water change (they started doing well for the first time off 6tbs but they were smaller) also they seem to have grown less in the past week but im not sure. i progresivly added more in 1tbs at a time but they only got worse which led me to changing the water again today
jtErA Reviewed by jtErA on . question? i started my plants more than a month ago but have had lots of trouble almost every new set of leaves eventually turns yellow and dies once they get to a mature size some of them turn yellow with little black dots. the plants are growing at a moderate rate and have alot of branches. but i cant get my leave to stay green. could it be that im keeping my 400 watt hps to close (little less than a foot) at first i was putting in too much nuits but now im not sure if im not putting in enough. the Rating: 5