Unsure what this is

[Bricson]

not sure what that web substance is on one of my Zoa's. The Zoa will open up and all, and doesn't look stressed but i'm a little confused by this. I don't see it on any of my other frags. Any clues?

Thanks

Water perameters-
NO3= 4ppm
Phosphate- .1ppm
calcium- 400ppm
light 8 hours a day
Using DI water.
running carbon/GFO

 

[SandJ]

It is a harmless sponge.