What's this stuff growing in my sump?

[ygon]

Its kind of slimy, started as a small patch and now seems to be spreading. Do I need to get rid of it or is it safe?

 

[johnanddawn]

Hard to tell from pics but looks like sponge to me which would be fine growing in your sump

 

[ygon]

Hard to tell from pics but looks like sponge to me which would be fine growing in your sump

Thanks. That was my initial thought but it grows flat on the glass and feels very slimy to the touch.