What is this on Hammer skeleton?

[OdinCorals]

What is this on Hammer skeleton? The hammer is a bit white from that side as well, is it effecting the coral maybe? Thanks all!

Base Parameters as follows;

NO3 - 2ppm
PO4 - 0ppm
Ammonia - 0ppm
Salinity: 1.025
Temperature: 80.6F

 

[izzyishh]

a sponge most likely you can scrape it off

 

[DSC reef]

Looks like sponge, harmless filter feeder

 

[KJ]

A+^^^