Outside Wall Treatment

[granny grump]

We have a block wall that surrounds our patio and it has been rendered. My grandson power washed it to get rid of the lichen/algae/moss that was growing on it quite profusely.
I want to treat it to stop the lichen/algae/mould returning and then paint it. I have seen numerous products such as Batiface but obviously I don't want to waste my time and money on something that doesn't do the job. I'd be grateful for any advice.