My reaction as well is that's not the flatworm eater. Hard to really tell from the pic.Its so hard with damsels, I doubt they did it on purpose. The second the get stressed, they turn dark, making it hard to see markings. I don't think that is a sprigeri.
Reef flux melted my bryopsis. Sea hare decimated my GHA. If flux does not work maybe try hare, but consider if it’ll get bullied by fishOnly a wrasse remain and can't catch him.
@Adauqua advise to use reef flux to elimiate yellow green sand and with gha. Added 20 capsules. View attachment 59828