Day 14 of Flowering: pH too high and leaves falling off

It is day 14 of flowering and the bottom leaves of my plants are slowly falling off. The soil pH is about 8. Plants are in Foxfarm ocean forest soil in 2 gallon pots. I'm flowering with a 250w HPS. There are 4 plants.

I am using the Foxfarm nutrients and following their feeding schedule. I've repeatedly tried to decrease the pH of the water/nutrient solution to 6.0 (using lemon juice) or even lower sometimes to compensate. The pH remains 8 even after doing this.
Nevertheless, the plants continue to show great vigor overall and initial bud production, so I'm not all that concerned, but I don't want this to escalate into a bigger problem.

Here are my specific questions:
Should I flush?
I've read a few forums saying that you should check the runoff pH. Is this a better measure than the soil pH?
Could this be a nitrogen deficiency? (i've actually tried adding some nitrogen containing nutes and it hasn't helped)
Not enough light on the lower leaves? (i've added 2 CFLs close to the base of plants to supplement my HPS)

same shit happened to me too, the PH is way off. I guess it's the temperature being too hot makes everything alkaline

It's best to check the PH of your water first...Our PH is so high here I have to mix 1/3 RO water w/ the tapwater. Also because TDS is so high in our tapwater it's necessary; rather than use PH down + tapwater.

PH lockout will do this...I had overly high PH in my first grow & about two weeks into flower, same thing. My plants had enough nutrients, they were just being locked out. Also a buildup of salts (high TDS) (lockout) will cause this; often w/ high PH tapwater this will happen in combination.....Too much moisture retention or poor drainage in/ of your soil will make these sort of issues worse than would otherwise be. Did you flush good right before you put them into flower?

If not, get some Clearex & flush those mo' fo's. -And start PHing & adjusting your water to where it's in the low 6's.