Should I clean?

[Box]

As title
http://i1204.photobucket.com/albums/bb418/Boxy1973/photo-90.jpg

[Garf]

Thats looking good. How long has it been going ? The general rule is as long as you can see the screen material, leave it to grow. A couple of days after the screen material dissappears under algae growth, then clean (in the early stages of screen development anyway).

[Box]

2 weeks running garf
I'll leave it and check in seven days
Cheers