What is on my coral?

[MuggyReef]

Recently picked up a nice size Zoa and another single polyp on a feather duster from Petco for $25. I realized it was completely infested with bristle worms, like 50-60 of them. I did two freshwater dips then a CoralRX dip and now there might only be a couple left so I actually took a look at the rock it’s on and noticed these two grey lumps. It doesn’t look like the Zoa, what could it be?

 

[kevgib67]

If I’m looking at the right thing, could be sponges. Harmless filter feeders.

 

[vetteguy53081]

Recently picked up a nice size Zoa and another single polyp on a feather duster from Petco for $25. I realized it was completely infested with bristle worms, like 50-60 of them. I did two freshwater dips then a CoralRX dip and now there might only be a couple left so I actually took a look at the rock it’s on and noticed these two grey lumps. It doesn’t look like the Zoa, what could it be?

Poriferan sponge. Inject with air or vinegar via syringe to stop its growth OT remove coral and pull off with a dental pick or small crochet needle

 

[Rick's Reviews]

Its inside colony if I'm not mistaken.

we don't have a Petco in UK. I would definitely avoid any further purchases if it has caused these problems ...
:(