To me it looks like poo with urates over the top but its kinda hard to tell. I tend not to worry over odd things like that unless it happens regularly or there is signs of illness.
I just set Swordtail's timer for his bath and paused it so I could actually fill his soaking bowl up and he crawled over my phone and canceled the timer
Mirage came out of brumation on April 26. He was doing great. On May 2 he started acting funny. We just redid his tank, and he keeps going into one of his hides. He just lays there. He shows no intrest in food. HELP!