That is for sure cyanobacteria and not a sponge.
Just your description, "i take it off and it keeps coming back", says it all.
No sponge is gonna outcompete gsp for space in an aquarium.
I hate to say it too, but your "strange morph" looks like regular old gsp that is starving for light and flow.
To get rid of the cyano, water changes and limit nutrients(cheato, less feeding, etc), limit photoperiod for a day or 3.
To get those gsp to show their true color and size, get some good lighting(this will also help with the cyano), gsp shouldnt be all shrunk up like that...
You probably have high nitrate and phosphate levels, dontcha.... Do you test?