Short answer
Pink or orange film in a shower is usually airborne bacteria feeding on soap residue, or iron in the water. Black is mould or mildew. White is mineral deposits or efflorescence. Yellow is usually soap, body oils or an ageing sealer. Dark patches that won't dry can mean water behind the tile. Most surface stains clean off; stains that come back fast, or grout that stays dark, are worth having checked.
Grout is porous (unless it's epoxy), so it picks up whatever sits on it. The colour usually tells you what that is.
Pink grout
A pink or reddish film along grout lines, drains and the tub edge is almost always a common airborne bacterium (Serratia marcescens) that thrives on soap and shampoo residue in damp corners. It isn't mould and it isn't a grout defect.
Clean it with a bathroom cleaner and a soft brush, rinse well, and keep it from coming back by squeegeeing after showers and running the fan for 20 to 30 minutes.
Orange grout
Orange or rust-coloured staining is either the same pink bacteria in a stronger colour, or iron in the water. Iron staining is common in homes on well water, which describes much of rural Ottawa. Rust stains also appear under metal shelves and cans left on the tile.
Clean it with a cleaner made for rust or iron that is labelled safe for grout, rinse, and use a water softener or iron filter if the water is the source.
Black grout
Black spots are mould or mildew. On the surface they clean off; if they keep coming back within days, or the grout looks dark from inside, moisture is getting into the grout and sometimes behind the tile.
Clean it with a mildew cleaner that is safe for your grout colour, improve ventilation, and replace mouldy silicone in corners, because mould grows into silicone and can't be cleaned out. If it returns quickly, regrouting with a sealed or epoxy grout may be the long-term answer.
White grout and white haze
- Hard-water scale and soap scum: a dull white crust, mostly where water splashes. Remove with a scale remover made for tile, used sparingly on cement grout.
- Efflorescence: a white powdery bloom where water has carried mineral salts out of the grout or setting bed. A little after installation is normal; ongoing efflorescence in a shower means water is moving through the assembly.
- Grout haze on new tile: a film left from grouting. It's removed with a haze remover suited to the grout type, soon after installation.
Yellow grout
Usually soap scum, body oils or cleaning products building up, and sometimes an old sealer yellowing. Deep-clean with a pH-neutral tile cleaner. If the colour is in the sealer, it may need to be stripped and resealed.
Dark patches that won't dry
Grout that stays darker in one area long after showering, especially low on a wall or near the tub, is often holding water from behind. Tap the tiles there: hollow-sounding tiles or a soft wall mean the waterproofing should be checked. (Patchy shading that has been there since installation is different: it comes from uneven mixing or cleaning water during grouting.)
Keeping grout its original colour
- Squeegee and ventilate after every shower. Dry grout doesn't feed bacteria or mould.
- Use pH-neutral cleaners for routine cleaning. Strong acids etch cement grout, and some bleach products can lighten coloured grout.
- Seal cement grout after it cures and reseal as the manufacturer recommends.
- For new tile, consider epoxy or high-performance grout, which doesn't absorb stains. See grout types explained.
Frequently asked questions
Is pink grout dangerous?
For most people it's a cleaning nuisance rather than a hazard, but it's worth cleaning regularly. People with weakened immune systems should take more care, since the bacteria can cause infections in vulnerable people.
Can discoloured grout be recoloured instead of replaced?
Yes. Grout colourants and colour sealers can even out stained but sound grout. They don't fix cracked or crumbling grout; that needs regrouting.
