Handling 30 metres of freediving line requires some care to make sure one does not end up spending 20 minutes untangling before each dive session. The double daisy chain (AKA double braid) solves this problem even for 200 metres of line extremely reliably and without hitches (pun intended :) )

Learning how to do this from a fisherman in Okinawa during the 2010 world championships has made me a happy man and it has become a part of all our Master and Instructor Courses.

We Freedive Alumnus and Generally suave guy Kevin Mitchell has put up a nicely concise video on how to manage your diving line and be trouble free forever.

KISS

I have one caveat and simplification to offer as an addition to Kevin's video

The final touch you added after securing the loops with a clove hitch requires an accessible working end. Without it, the double daisy chain (or double braid) can be used even in the bight, i.e. with both ends of the line busy doing other things. I only ever use the clove hitch to secure the loops and have not yet been in a situation where they came loose by accident, so the clove hitch alone has been secure enough in my experience.

The added advantage of being able to the double daisy chain as a flexible, reliable and quick line shortening device, for example in tether lines between floats, easily makes up for the, apparently negligibly reduced reliability of omitting the final step in the video. 

Without further ado, here is Kevin Mitchell: