sunstone also carrys the calibration soultion or if you will (buffer solution) its around 1.50 per pouch a cpl of pouches of each will finish your grow with some leftover, word to the wise it takes about 5 mins to calibrate a ph meter i have learned the hard way to calibrate weekly or at every resv change its not essential but considering the rewards, i use a tiny shot glass a few drops is all it takes to calibrate
as far as ph down i only use vinegar carefull with the down