My tunnel is about 8 years old and firm and good but I have awful algy on the outside. I have tried washing up liquid and Domestos bleach but the green algae (and black on the top) remains. Jeyes is not to be used on it (so the tin says) . Can you please suggest something to wash the tunnel with? I use a window cleaning sponge on a long handle as my tunnel is tall and I cannot reach the top by hand
Many cleaners have solvents in them and cannot be used as they tend to shorten the life of the plastic, causing it to break down earlier than it should. Even rubbing with the window cleaner can cause tiny marks that may weaken the polythene.
Too much shelter tends to make algae worse on a tunnel. The options are to leave it be, with reduced light, or to re-clad and clean it at an earlier stage.