That's what I thought, thank you for confirmation!Sponge. I have had a few of those too recently. I pulled off a large one and planted it where I could watch it for a few days and then tossed it into the sump. After a few water changes and no amino or trace dosing they diminished to normal growth. By observation I would that the corals were not fans of the same parameters that made the sponges grow fast. If I see that kind of sponge growth, now I know to do a 25% to 40% water change.
It was neither nitrates nor phosphates which continue to stay at undetectable levels. I believe it was from trying to feed my tank until I saw nitrates and phosphates. Obviously, that does not work.