Hey Greech! You are right...chaetopterid....I found clear pic online... I posted pics that were just WAY to large for you to see anything clearly.
1st pic above is bottom of a piece of rock about 9 in long,(the far right 1/3 of the 2nd pic) I think the extensive spread of the 'tubes' is clear.
The 3rd pic is zoomed way in to the lower front rt corner of the aquarium. The lines below the sand surface are the worms themselves. In the center you can see a columnar shape...the worm continues to build it's tube.
The white filamentous structure that looks like a hair protrudes from the end of the tube. I know there are some algae issues and am working toward getting rid of that,but was mostly concerned with the sudden spike in toxicity.
BTW, the nitrates have dropped considerably, just barely above where they need to be. Am being patient as all seems ok.
I am not a very good writer and I believe that fact added to the problem...you also read my posts as a current snapshot of the population. I have 2 denali cardinals, 1 percula clown, 1 dwarf Lion, a couple small blue legged hermits and a feather duster(which I didn't mention earlier) The Rusty Angel and 2 coral beauties were put into the story only in terms of history of the tank. They were never all in there at the same time. My description of the timeline is horrible and I apologize. I also noted that in one post I said I had 20lb sand then later in same post 30 lb. I have 30 lbs. Actually its very course globs now thanks to these wormy guys. Manually removed a bunch of the algae and some hydroids(?) and will get at the cannister tomorrow(I hope!) Currently using Ultra Zorb charcoal product- is ok as opposed to GFO?
So grateful for your patience and help with both the ID and other valuable info. This tank has been chugging along for 3 yrs now and all of a sudden 1.Coral Beauty died, 1week later an relacement coral beauty died then after more water changing and canister cleaaning ,filter material relpacement, the rusty angel died!!! Guess I panicked a bit and not thinking, tried to post billboeard sized pics! Lessons learned!