ph pen

I just got my ph pen and tested the water I have been useing. the water is 8 to 8.1 with out additives. I tested the water drainage and it tested 7.9 Am I correct in thinking that this is the problem and adjusting ph to 6.5 would help but doing it to fast will shock the plant? I went to lowes and home depot and they did not have ph up and down. Should I order some on line or is it ok to use lemon juice to adjust ph level?

Where did you get the "pen" at?

you can gram PH adjusters at pool supply store... Fish (pet) Store or local grow store...