Hey folks. I have a full size fiberglass shower/tub unit in a home I am renting. If you look close you can see it has a lot of soap scum and the Scrubbing Bubbles doesn't do a whole lot to remove it. The Scrubbing Bubbles just cleans a little bit of it off. I can run a fingernail through it so it is soft soft scum, not hard water buildup. Do any of you know of a strong cleaner that is commonly available that will work? I don't mind wearing a mask and gloves to do a deep cleaning. Thanks!