engineer goby spitting out fuzzy balls

[54seaweed]

I never seen him do this till I moved him into the new 90g tank
he seems fine in every way eats swims around burrows through sand ect
this is the second time I've seen him spit out a fuzzy looking ball
just wondering what it is I've noticed my serpent star munching on it just want to be sure it's not anything that will cause harm to the other tank mates
I tried google with no results

 

[Sniperhank]

Probably an algae or something that came out of the sand or his cave I'd assume.