My rule of thumb is use a prespray 10ph or less on Nylon, usually Bio-break. Reason being is the dyes in Nylon can be be affected by alkalinity, just like wool.
Local company turned a white Nylon Home Depot carpet yellow in a ladies house and didn't know how to fix it. They recleaned it a few times but same result. They had to replace the whole house.
I run an acid rinse on every cleaning, usually flex ice. I use to be a soft water only guy but I can really tell a difference with flex ice. The main difference is when I go back to some of the repeat accounts I have, they look great! I don't get to put down protectant most of the time, so I know it's the rinse.
Now, I will admit, I'm not sure if this is true for ploys and olefins, just the majority of Nylons I clean.