These tunicates are short lived and spend only a few hours in a larval state before attaching to a suitable substrate. From this I gather there must be one or more colonies in the tank which have spawned since I last cleaned the Tunze pump they have settled on.

They do not like strong currents but seem to be happily settled on the pump and the pipe.

All tunicates are planktivores so it may not be coincidence that these two colonies have appeared since I started dosing Cyclop-Eeze