Caustic soda?

I'm with the bleach brigade too, I either use bleach, stardrops/flash or Zoflora, they all get rid of the nasty green slime, hubby always uses the pressure washer. I have to be very careful because if the hens,I wouldn't use caustic soda unless I had a blocked drain to be honest. Happy scrubbing!

 

just remember , any worms that come to the surface dont leave them lying around for the birds to eat