Not sure I use bleach then a pressure washer it keeps it at bay for a good while

Is your patio in shade or constantly damp? May be this needs to be addressed? But I agree I use bleach too just make sure you wear high Wellies and dont walk it on carpets.

I use bleach too,and a good strong brush.Just have to be careful to not let it run on to the soil and plants.Haven't used our pressure washer for a while,after I saw how much the next water bill had increased,as on a water meter.!! Use it from water butts now if full..which is most of the time these days:o))

My patio meets the lawn and a couple of flower beds never kill any thing off yet. I use a stiff brush, bleach and a bucket of water and go back and forth till its sort of moving, leave over night then I hose it off. Dont laugh but I do mine once a year in the spring, just after the clocks go back so its light enough to do quite late when no one else is in the garden. I get up early and wash it off.

Good idea about leaving it overnight Drc,will do that myself this year..thanks.The north facing paths are worst as mostly in shade..and thats a lot of mine,so hard work,but looks so good afterwards.:o)).

Thought it must be shady as you seem to have so much.

Thank you all for your tips! Although I call it a "patio", it's actually a large yard with high walls which I have made into a patio area - I have no lawn and usually grow my plants in containers and hanging baskets. Although I get the sun all day, parts of it are often in shade which may account for the problem. As soon as we get some decent weather I will have a go with the bleach, stiff brush and pressure washer. No easy cure here then....lol.

Is your patio wood because there is an anti slip fine sand you can paint on wood such as sleepers, one of the members told me about? I will find the question for you if it helps?

Not wood Drc726, it's concrete. Thanks anyway ...:o)