Is this something to be alarmed about or I'm overreacting again?

OK I watered today, waited for it to drain and took measurements. The PH level was/is 7.2 is that too high? Should I use distilled water in future or should I just flush now?
What's concerning me is also that the leaves are yellowing, at least under the HPS light, they look light green under normal room light.

Isn't soil ph supposed to be around 6-6.5?

I am using this pH meter: http://www.amazon.com/HM-Digital-Waterproof-pH-Meter/dp/B00132G102/ref=sr_1_4?ie=UTF8&qid=1312288764&sr=8-4
and here are some calibration solutions. Not sure what brand you have - Hanna I think wants to calibrate to a 4.01 or a 7.01 solution, while others are fine with a 4.00 and 7.00. I used the 7.01 for my meter above, which wants to calibrate to 7.00. However, I am not *that* worried if my readings are off by 1/100th.
http://www.amazon.com/General-Hydroponics-7-0-Calibration-Solution/dp/B001D0CKYK/ref=pd_bxgy_hpc_text_b
http://www.amazon.com/Hanna-Buffer-Calibration-Solution-500ml/dp/B000CRHKZY/ref=sr_1_2?s=home-garden&ie=UTF8&qid=1312288908&sr=1-2
http://www.amazon.com/Flora-Hydroponics-Buffer-Calibration-Solution/dp/B004TRPU0A/ref=sr_1_10?s=home-garden&ie=UTF8&qid=1312288908&sr=1-10