Dark / black spots on rock work

[Digitalfirex]

I have noticed some black or dark spots on random rock work. Can't ID. Any ideas?

 

[lapin]

Could be sponge or begining of new alage

 

[Digitalfirex]

Could be sponge or begining of new alage

I did have a bit of cyano I was fighting. I used chemi clean for the 48 hour treatment. Water change. Bacter7 and now schedule skimmer off 1 hour everyday. Still have GHA in tank I'm trying to clear, this showed up after. Past week? Should I scrape off?

 

[lapin]

what ever it is, it liked that you killed off all its competition with ChemiClean. I dont know what it is so removing/scraping it off it might be best

 

[Digitalfirex]

what ever it is, it liked that you killed off all its competition with ChemiClean. I dont know what it is so removing/scraping it off it might be best

Got it, that makes sense. Thank you.