It's a good idea not to place stressed plants into flower. It usually compounds the stress.

What are you using to test the ph? Ingoing water should be between 6.3 and 6.8 for a peat-based soilless mix, for the entire grow. (veg and flowering)

Do the directions say to use the nutes every third watering? Sounds like too much. No guessing, follow directions.

Is your soil the Fertilome Ultimate Potting Mix? If so, there should be no problems coming from there.

Are the leaves that are falling off from the lower canopy? (twords the base) If so, could be the leaves aren't getting enough usable light. If the upper canopy is growing fine, perhaps lighting is also an issue. 6" is too far away for 23w and 26w CFL's. What are your bulb wattages, and what color is the light when they're on? Yellowish or blueish?