Wait, why do you have three probes? Well anyways, the probe should be place on the heat tape and the tub should hover above it with out moving it. So if u tape down your probe make sure not to tape any of the metal part of the probe. As far as tubs and holes, I put 4 holes some people do two some ppl do none some put to many lol, totally up to you. Also, sometimes the tstat has to be set up higher. Example: I have to set mines at 110 to get a reading of a 88-90 in the tub. This is of course in a room with a temp of 65 degrees. So now when my room is at 69-70 I can set my tstat at 106 to get a 88-90's in the tub.