Adjustable Ballast settings

[Marihuanero]

I've got a Quantum ballast hooked up to a 600w Hortilux bulb mounted in a Cool Tube cooled by a 6"duct fan. This is inside a 4' x 4' x 8' grow tent.

There are 3 Afghan Kush plants and 2 Blueberry Mystic inside the tent that are currently in flower, they've been there for 38 days now, and are getting heavy with buds by the day.
Now the plants themselves are starting to show a few fan leaves that are drying out and curling, I'm inclined to think it's a natural part of the plant developing buds, some of the plant tops have grown and are about 6" or 8" from the bottom of the Cool Tube.

I water them about every other day making sure not to over-water, I've been using Fox Farm nutrients as directed.

My question is whether i should cut back on the strength of the lighting as the ballast has a few settings that are like 50% or 75%, should I cut the ballast to a lower setting at some stage during the flowering process?

 

[MrGhettoGrower]

Yo your leaves are gonna be dying at the 5th week of flowering~
I wouldn't worry bout the lighting as much as watering every
other day is a little much and in the long run the roots will begin
to rot later in the flowering stage this will git yo drooping and a
really bad looking leaves with claw fingers...........

 

[Marihuanero]

Yo your leaves are gonna be dying at the 5th week of flowering~
I wouldn't worry bout the lighting as much as watering every
other day is a little much and in the long run the roots will begin
to rot later in the flowering stage this will git yo drooping and a
really bad looking leaves with claw fingers...........

The leaves on the two Indica strains, Afghan Kush and Blueberry Mystic are yellowing, browning and curling and that's on the sets that are 2 or 3 levels down from the top, the bud formations look nice and healthy though. So I should just concentrate on watering and forget about adjusting any light levels?