I am trying to get my ghl to control the ph in my ca reactor. I made a socket function for ph set to decrese.

then i set the normal value to 6,63
hysterix to 0,1

this makes the co2 go on at 6,69 is this the normal function? so if i want the ph to be kept at 6,63 i need to set it to 6,53 ? or am i doing it wrong?