Well it’s not quite fungus, but a rather heavy case of soapscum…I’ve tried Kaboom but it cleans in streaks. So now my tub has clean streaks and grey scum.
Are there any household products (ala Heloise) that work better? Any store-bought products?
Kaboom is advertised as “a healthier alternative to ammonia-based or acidic solutions.” In my experience, that’s often linguistically equivalent to saying “it doesn’t work well.” The MSDS (pdf) for the product lists 5-7% Urea-HCl as the main ingredient. Urea is a fairly good solubilizer, and denaturant, but it’s not known for its ability to dissolve calcium (etc) salts of detergents, i.e. soap scum. Get yourself an acidic cleaner, something with acetic acid, citric acid, or sulfamic acid listed as an ingredient. These acids are weak enough that they’ll dissolve the scum, without harming your tub.
I just use a ~2% solution of citric acid to break up scum. Vinegar, straight from the bottle, will also work, but not as well as citrate.