The probe is sold separately even if you purchase the pm1 on line..the pm1 brand new will cost you $85 and the ph probe will (if you buy a lab grade) $69..
If you going to purchase an Apex do your self a favor and buy the full unit that way you won't need a pm1 cause the base unit will have an outlet for a ph probe so you won't need a pm1..I only bought the pm1 cause I only had an Apex jr and I just recently set up a calcium reactor,then I ended up upgrading to an Apex full unit..