Thanks alot for your help, Swizzy. So here's what I've got/done:

Current nutrients list (25 gallon system):
10 mL/gallon of Fox Farm Grow Big
5 mL/gallon of Earth Juice Catalyst
25 mg/liter Sodium Meta Silicate
1 teaspoon/gallon Epsom Salt

I haven't really seen any improvement in the leaves, and there's now actually some downward curling on some lower large leaves that's visible in these pics. However, new growth seems to be coming in fine. The current ph is just above 6.05.

I measured, and at the current height there's about 6-7 inches between the plant and the HPS reflector, with 13 inches from the plant to the light bulb. I haven't changed the height of the reflector at all yet. Maybe raise it 6 inches?