Why won't soap scum come off my shower glass?Updated a day ago

Soap scum that will not come off shower glass is usually one of three things. Soap scum itself is a film of soap and body oils on top of the glass and it does come off with Koh Bathroom & Shower Cleaner, a longer dwell and gentle agitation. Mineral build-up is calcium and magnesium from hard water dried onto the glass, and it takes repeat cleans and mechanical work. Etching is permanent damage in the glass surface itself and no cleaner removes it. Two quick checks tell you which one you have.

Three things look almost identical on a dry shower screen, and they behave completely differently. Working out which one you have is the whole job, because two of them come off and one of them never will.

Two checks. First, run your fingertips across the cloudy area when the glass is completely dry. Slick or waxy suggests soap scum, hard or gritty suggests mineral build-up, and perfectly smooth but still hazy suggests etching. Second, clean one small patch properly with Koh Bathroom & Shower Cleaner, rinse and dry it, then compare it to the glass around it in daylight. A patch that is clearly clearer means the haze is removable. A patch that looks identical to its surroundings means etching.

For soap scum, spray Koh Bathroom & Shower Cleaner and let the foam sit for 5 to 10 minutes, which is longer than the usual 2 to 3. Agitate with Koh Ultra Pro Bathroom Mitt in firm circular strokes, rinse thoroughly with water, then dry with a clean microfibre. Heavy soap scum often takes two or three passes rather than one. For stubborn patches, step up to Koh Diamond Sponge with light pressure and plenty of water.

Mineral build-up is calcium and magnesium, and Koh Bathroom & Shower Cleaner is alkaline at pH 8, so it is not a descaler and it will not dissolve mineral deposits the way it lifts soap scum. What shifts mineral build-up in practice is repeat cleans with a long dwell plus mechanical work, using Koh Ultra Pro Bathroom Mitt and then Koh Diamond Sponge with light pressure and plenty of water. Koh does not recommend acidic descalers on shower glass, because acidic products are the class of cleaner glass coating warranties most often exclude. If you use one anyway, check it with your glass or coating manufacturer first, never combine it with another cleaner, and keep it off stone.

If the clean-patch test showed no improvement, it is etching, and no cleaner removes etching because the damage is in the glass surface rather than on it. There is nothing sitting there to lift. Realistic options are professional glass polishing, which is a specialist restoration service that sometimes helps on light etching, or replacing the panel. Prevention on new or restored glass is squeegeeing after every shower with Koh Bathroom Squeegee, drying the seals and ledges, and never letting hard water dry on the glass. A protective coating applied by the installer also helps.

If you have worked through the checks and Koh Bathroom & Shower Cleaner is not doing what you expected, get in touch with the Koh team. Send a photo of the glass and a short note on what you have already tried, including which of the two checks you ran and what they showed. The team can troubleshoot the specific screen, and if the product is not right for your situation it is backed by the Koh 30-day money-back guarantee.