THIS. VIDEO! These are my opinions about the song/video and what it might be referencing.
We first see Josh and Tyler by this empty pool and then this little creature (Ned) comes out behind a car door (possibly a reference to the car they set fire to). He looks into the pool and isn't happy with it and hides behind the door.
Josh and Tyler then pour more water into the pool but Ned still isn't happy (possibly referencing fear). Finally the guys get this huge thing of chlorine and Ned jumps in.
Does this represent fear of the unknown or maybe his writing? "Sippin' on straight chlorine, let the vibes slide over meThis beat is a chemical, beat is a chemical..."
Whatever it means, twenty one pilots did it again, blew me away!