Gotweed- I know pH pens well, and they autocalibrate for different solution temperatures, not for pH itself,... not that I necessarily think it's off, but you can't use other random liquids for calibrating, it must be a specific, stable solution made for this purpose...it's readily available, and some should have come with the pH meter when you bought it...
but from google i found someone who had ph checked their water at different concentrates and for my concentrate the water would have ph of around 5
...sorry mate, but no correlation can be made between what some other person gets and what you get-- water is not the same, in ppm's, pH, etc.,... and a pH of 5 is waaay to acidic for feeds! ...epsoms will be fine, but keep in mind that they are MgSo4 only, no Ca in them (foliar spray at 1 tsp/gal),...****

whoa! holy crap, what is that stuff you posted?
Yes, there's also way way too much N in there (N= 15%), but worse, the Ca source is CaO- calcuim oxide, also called quick lime... it's caustic nasty stuff,... I don't know what that fert' is really for, but if you use that on your MJ plants you'll be taking an awful risk! Absolutely not recommended! Find another source of Ca dude,...