Hi, I'm looking for advice on cleaning bathtubs. I've been using Scrubbing Bubbles & have had no problems. I've been mostly cleaning lower end/older homes. Now I'm starting to clean newer homes. I've read that Scrubbing Bubbles & lots of other chemicals can scratch acrylic bathtubs. I also can't really identifier acrylic from other materials. What do other people use for cleaning bathtubs?