plant leaves failing!!!!! help

ok ive ben growing this plant for quite a while it was my first grow and dont know much about what to use... i planted it in a 3 gallon bucket in miracle grow soil i water it about every 3 days and on ocasion ad miracle grow drops into the water the plant is about 2 ft tall and the bottom leaves are slowly turning yellow at the tips and then black!?! most of the bottom leaves are dried up and shriveled and fallen off the plant. im also using a 70 watt hps light right above the plant and the light isnt making it to the bottom leaves as much as it should...

is this bad my leaves are doing this and if so what do i doby the way humidity is 55%



here is my most recent post there are some pics you can kind of tell on the plant
https://www.rollitup.org/general-marijuana-growing/114765-male-female.html

GROWFAQ
sorry those pics don't show me much. check out the link and see if u can match it up. as for ur light, even a 1000wat hps only penetrates well for the first foot or two after that it fades drastically