What is this pest

[cocowizzz]

I was out of town and didnt change my water for 2 weeks I need and a few things grew some I know some I don't what is this one kinda looks like a sponge kinda looks like a clump of cyanobacteria could be a montipora coral any thing helps reefers!

 

[Brad Miller]

Looks like a clump of Cyano to me

 

[408Dartfish]

Looks like cyano

 

[Dancingmad]

+1 Cyano. If you think missing a water change is the issue I'd go with manual removal and your standard maint regimen - suck that joker off the rock when you do your normal WC .