How do you remove built up old soap off of the tray in the shower?

very hot water that has baking soda added , leave for 1/2 an hour or so and start scrubbing, emptying it out every so often, also add ammonia with the baking soda if needed , they are both very good breaking up soapy deposits. it may take a liitle time , patience is a virtue

I would just take a nice long shower and scrub away. Our soap dish gets caked up like that too and i just wash it all away with my fingers. I never heard of it being so dried on though, that's crazy.

How about taking a rag dip it into boiling water and let the rag lay on the dish. Go back every 5 minutes or so and pour more hot water on it. Maybe the steam will help it come up.

Just a shot in the dark, but maybe try to melt it with a hair dryer.

Another shot in the dark, but I clean soap scum with Clorox. If there were a way that you could keep some on this buildup overnight maybe it would eat away at it.

Get some steel wool and scrape away! Just be careful if you're worried about the surface getting damaged because it can be pretty abrasive if you push too hard. But since you were considering using a scraper i'm guessing that isn't an issue.

when soap starts to build, i just let hot water fall on the tray, it makes it soft and easy to remove.

Use the green scrubby side of a sponge.=)

KABOOM!