ID help, 1 colony with 2 issues

[boacvh]

I posted this question on my build thread as well, but posting here in case more people see it. Total noobie here.

I got a zoa colony a few weeks ago, dipped it for around 10 minutes in revive. It was completely hard to the touch and I brushed it as well. But now in the water after a few weeks of doing great I just started noticing like something has grown on the back of the colony rock. And it looks like some kind of brownish soft tissue that grows and retracts with the flow. Any ideas what this brownish sack could be?
The zoa colony was doing great, but now I am inclined to just take it out of the tank....

The second issue/question is the zoa’s look like they have a blackish mat next to them now. One can see it when they retract. Hopefully you can see both in the pictures below, can someone help me ID these 2 issues?

Brownish sack on the back:

Blackish “mat” can be seen when the polyps retract:

 

[Dr. Reef Verified Sponsor]

Maybe a sponge but a better pic can help id it properly.

 

[Lovemyreef2015]

I'm going to say its sponge as well.

 

[reef lover]

+1 sponges. Should be easy to remove if bothering the zoas.

 

[boacvh]

Maybe a sponge but a better pic can help id it properly.

Thanks! I’ll try to get some better pictures today and will share.

 

[boacvh]

+1 sponges. Should be easy to remove if bothering the zoas.

If I may ask, how should I remove it? It seems to be encrusted to the rock. Just rip it out?

 

[Sea MunnKey]

It's Black sponge and they spread & suffocate over anything in it's path. They're easy to peel off ... I use the back end of my tweezers

 

[reef lover]

+1

 

[boacvh]

Thanks everyone for the help. Here are a few more pictures.