Can someone tell me what this is?

[laurenseitz]

Two of these appeared about a week ago and have continued getting larger. I'm not sure what it is and I was hoping someone knew and could let me know if it's okay in my tanks! Thanks!

[TangingOut]

Sponge, harmless filter feeder.

[Denbf58]

+ 1 on sponge as tank matures you will see them all over different colors pinks and yellows too

[Mcgeezer]

Sponges are an indication of good water quality. Pat yourself on the back.