Topic: How do you remove ...

[Slug_killer]

 ... algae from inside the plastic of a triple walled polycarbonate coldframe ?

[manicscousers]

we use vinegar, washing up liquid and warm water with a car sponge  :)

[Slug_killer]

I don't think I'd be able to get the sponge in the little tubes, but I guess I could fill the bath with a vinegar mixture and soak it.

[manicscousers]

ah, sorry, maybe I'd be best reading a post properly  ;D
I've no idea, unless the soaking works, sorry

[tonybloke]

pressure washer should do it!!

[Larkshall]

... algae from inside the plastic of a triple walled polycarbonate coldframe ?

I would suggest using a "Pull Through" as used for gun barrels. Get a length of fine nylon cord, a strip of lead, insulating tape and sponge. Take the cord (a little longer than the polycarbonate tubes), tie a not in each end, tape the thin strip of lead on the cord (if you haven't got lead, a nail will do). Fasten a piece of sponge (slightly larger than the tubes) on the other end. Drop the lead/nail down the tube, then pull the sponge through. Do this for each tube. Bleach will help to kill the algae.