Any Idea What on Earth this Is?

[Hair Algae Wizard]

Folks,

Noticed this morning during my usual morning tank viewing, some odd stuff attached to the underside of my rock. None of this is currently on the top side of the aquascape, just underneath. It wasn't there yesterday. Any idea what on earth it is?

Tank is about 90 days old now, with 5 Anthias and a clean-up crew.

Pardon the pic quality, this was the best I could do.

 

[Redfoxtang]

Looks like bubbles to be honest.

 

[Zach W]

Just looks like trapped air bubbles on the underside of your rockwork!

 

[Archibald J McLauchlin]

Air bubbles

 

[Hair Algae Wizard]

Thanks guys, I was worried it was the beginning of something bad! I've never seen this before, so it threw me.