Equation for ph control

Hello,

i use Matlab r2013a and want to create a fuzzy logic adaptive pid control with simulink. I want to control the ph value for example i got an input of 10 and the control shall regulate it to get a neutral ph value of 7. I already created a control (but not for 100% sure if the control is right) and used rules for the fuzzy logic which i found in the internet. My problem is how to figure out the right equations to get the control to work. Does anyone can help me?