Why would you hook up a zinc anode? Hopefully, you are NOT trying to protect a non-salt pool heater that way?

Going to 1.5" => 2" => 1.5", won't cause problems, but you probably won't gain anything, either. I'd have to see your pump pad layout to be sure, though. You should include pump and filter make and model info, as well, but you can post that in your response here.

If you want useful responses, you'll need to sketch your plumping layout plan, and scan or photograph it, and then send it to poolforum@gmail.com . Gotta say, I'm pretty skeptical however.