09/11/2026
Please stop putting bleach on your patio. I'm asking nicely.
It's the most common piece of advice on the internet and it's wrong in four separate ways:
It doesn't kill the root. Bleach oxidises the surface colour of algae. The organism underneath is fine. Your patio looks clean for a fortnight and then comes back and you conclude you need to do it more often, when you actually need to do it differently.
It eats your pointing. Sodium hypochlorite at household concentration degrades cement-based jointing compound. Every treatment costs you a bit of structure.
It runs off into your borders. Whatever's planted within a metre of that patio is getting it too.
It stains natural stone. Indian sandstone in particular will go blotchy and it does not come back.
What actually works is a proper biocide at the correct dilution, applied and left. It looks like nothing is happening for two or three days. Then it's gone, and it stays gone for a year or more, because you killed it rather than bleached it.
You can buy the stuff yourself. I'm not gatekeeping it ask in the comments and I'll tell you what to look for on the label.