I didn't when I used stainless tanks. When I started using a JOBO, I noticed uneveness and air bells so I decided to do a pre-soak. Then I went to the JOBO site and saw that they recommend a very long pre-soak of five minutes so I went with that. Since then I read an article that said long pre-soaks have varying unpredictable effects on different films but I haven't returned to a short pre-soak as of yet.

I use tap water for the pre-soak for the same reason that you mentioned.

-Neal