How to clean the downpipe?

[hsp]

Well, maybe the answer is that I don't have to clean it. But the buildup in my 2-year-old Red Sea Reefer Max G2+ 300 concerns me. Everything is stable in the DT, and I have no acute problems, but if the growth continues, will it eventually close the pipe? How can I clean it without disassembling the plumbing for hours to soak it in citric acid?
Thanks for any suggestions!

Here is a short video with more details:

 

[mann1139]

Quick pass with a tube brush will make short work of most things that will grow in there.

 

[Boehmtown]

I don't think it will ever close. BUT I had a shortish power outage once. That tube dryed out and killed off a bunch of stuff that was in there, blew my phosphate up into the whole numbers.