New Tank - White Fuzzy Thing On Rock?

[ShatteredPhoenix]

Hey All,

Is anyone able to help me identify what this white fuzzy looking thing is that’s started growing in my rock?

A bit of context:
I am new to saltwater aquariums and I started this tank about 4 weeks ago. I’ve used Dry Sand and Dry Rock with RODI water to fill it up initially.

I dosed it with 15ml of Ammonia once, waited until that was all turned into Nitrites and Nitrates and then dosed it again with another 15ml of Ammonia.

After doing a recent check, the Ammonia has gone back down to 0 as expected with all other parameters being within the expected range.

I haven’t added any fish yet, my skimmer isn’t turned on and I haven’t set up any lighting yet either.

I noticed the thing in the picture starting to grow on the rock recently and was wondering what it was, considering the tank is practically new with nothing in it.

Thanks in advance for your help,

 

[Crabs McJones]

Is it hard or soft, almost looks like coral skeleton of some sort. If it's soft it's likely tunicates but hard to tell from picture

 

[Devin6871]

That does look like the skeleton of a favia to me

 

[ShatteredPhoenix]

That does look like the skeleton of a favia to me

Thanks - I did some google searching and confirm it matches the profile.

This must be a leftover from the previous owner of the rock and his tank setup.