Growth I'd please

[Twoddler]

Hi all, I'm just about to do my bi weekly water change on my fluvial 13.5. I've noticed this growth in the last couple of days.
Should I take the rock out and scrub or leave it to the cuc

 

[Idoc]

Without taking the rock out, maybe use a toothbrush on it. Possibly it's a black sponge growth.

 

[JGT]

That’s a form of bubble algae. Remove the rock, scrub, wash off with tank water and return the rock to the tank. Scrubbing in the tank will only cause it to release spores resulting in., you guessed it... more bubble algae.

 

[Twoddler]

Thanks for your replay, It is easier to remove the rock and scrub in the old tank water so I think I'll do that.