Every now and then the tube worms get a fluffy collar. The amphipods seem to like it but what is it?!?

Lol thatll be one of those complicated questions. Tubeworms vent iron hydroxides in ferihydrates, that and a touch of organic slime creates a perfect environment for a type of primitive fungi and bacteria, and copepods and amphipods love the stuff, whole deep sea systems and vents use it as a food source. Not harmful as long as there isnt tons of it. Yours is being handled by scavengers, so no probs, if that wasnt happening you probably want to remove it. Might also be a sign iron levels are creeping up.

Lol , I think youre on you way to a non light dependant marine colony.

that's so cool! Cheers LHG, I'd have never found that out via google

Lol you probably could have, using iron to provide seeding for phytoplankton is big news at the moment. Its all kinda connected research. You'd be amazed what a little iron in seawater can do in regard to causing a massive proliferation of microfauna.