The Fellow at the Hydro Store gave me a Dutch Nutrient Formula EC Buffer that reads EC 2760 MMHO Buffer. I've got no idea whether this should be used with the Hanna Instrument or if it will even calibrate it.
I've kind of been going off how my girls look. They were beautiful for the last couple weeks but I've started to notice their leaves yellowing ever so slightly and therefore bumped the PPM from 300 to 450. I'll watch over the next couple days to see if any difference is made.