I use a good high ph presoak designed for touch free autos for my SS presoak. On liquid HP
soap I use something with good show. A HP
soap that has a little alkalinity will prevent scum buildup problems in the tank, but by the time it's diluted several hundred parts to one in the water stream there is little effect on the surface of the car.
I sometimes use low ph foaming conditioners for foam brush to also prevent buildup and foam generators from clogging. The scum/algae buildup in tanks occurs in an environment where ph is greater than 4 or less than 10, so if you get outside that range it prevents issues.If used in proper sequence by the customer it produces a great looking car. The touchless alkaline presoak will cut through film on the paint, and the low ph foam brush used afterwards will help reduce alkalinity and make glass and chrome shine better.