I agree with Kitty, upgrade your lights to a 400w system and buy two bulbs, a Metal Halide bulb for vegging and a sodium bulb for flowering. If you can go for a coolshade light that couples to your extractor fan for super cool growing.
The heat lamp you have at the moment is not suitable for worthwhile results, and has caused your girls to strech and have limited a amount of leaves. The Mercury Vapour bulb also produces a great deal of heat, and puts out about 1/10 of the lumens a metal halide bulb. Try not to trim any more leaves. The white spots may well be heat stress related, can be an mg deficiency, but usually the leaves curl up at the ends, hence the phrase "praying for mg". May also be related to your fungus Gnat problem.
As for the sodding fungus gnats, I think everyone has had problems with these fucking things this year - both in the States and the UK. Best cure is to use the old sticky traps to catch the adults, and treat your soil with Gnat Off. It stops the larvae, that live in the soil and feed on your roots causing problems with nutrient uptake and inviting disease, from eating. I had my grow room sorted in a week.