I don't think it's heat stress, because temps are not that high and plants are not that close to the lights. Other than the burnt tips, they actually look good (to me, which might not be saying much).

I don't really understand how this form works so I shall do my best:

H= hydro - Fafard's potting mix with extended release ferts


E-indoor
E-soilless
E-Fafard's Container mix (extended release ferts)
SCL- about 20% perlite
SCLR-Soil or slab runoff pH
E- tap water, pH 7 plus or minus .2
E- plants 5 weeks old, 9 days into flower
E- Botanicare Pro Grow (during veg), Pro Bloom (now), Sweet and Liquid Karma (since the beginning)
E- watered about every 3 days
E- 138watts of CFL, about 3" from tops of plants
E- ambient temperature is usually 70-73F
E- having trouble with humidity, usually 60-70%
E- 12/12
E- computer fan for circulation
TR-Did you pre-soak your media in pH corrected solution? no

Within the next few days plan to add a few more lights, and a bathroom fan to help control humidity levels (and possibly temp. if that becomes an issue with increased lighting). Also, I didn't read runoff pH last time, but the time before that they were lower, about 5.5, so this last watering I added some pH Raise.