It is growing all over my sand bed even in shaded areas and does not respond to changes in lighting. It has remained the same regardless of increasing or decreasing the lighting.
It started after I ran out of RO for topping off my tank. I could not get to my LFS due to my schedule so I used distilled H2O I had on hand. A couple of days later I went away on a trip. I returned finding the sand appearing like my attached photo. My housekeeper, who has a tendency to overfeed, took care of my tank while I was away. My tank is two years old and with the exception of an outbreak of hitchhiking bristleworm has remained issue free.
This "gunk" has affected my alveopora (I don't think it will survive) and leather coral. It has had no effect on my frogspawn or zoanthus. Interestingly my caulastrea is thriving. My clean up crew is unaffected and snails remain healthy.
What has puzzled us in identifying this are two traits I have not seen in my research. 1). As I mentioned before I had an outbreak of hitching bristleworms and have been successfully eradicating them with traps. Horrifically, I have witnessed the worms being cut to shreads by this "gunk" when the worms crawled across the sand and 2). It stung my partner on his thumb two days ago and the thumb is still numb! His description of the stuff is a "booger with 4 to 6 hairlike appendages which it casts out as if it were fly fishing snagging the worms" (beware: do not read this late at night).
I have increased my pH, reduced feeding and plan to remove all the sand and go bare bottom. I have a Harlequin shrimp so can't use hydrogen peroxide. Please advise. My fish have been unaffected.
