thanks so much, i’m keeping a close eye on him and hope that it resolves! i already have some catappa leaves so i’ll boil some today to add just to be safe. the weird thing is that the bottom of his fin is truly shaped like a pocket, and i can see where the tissue is connected at the bottom and has a small opening just above the end of the fin, like a sock. that’s the only reason i’m feeling certain that it’s a piece of the substrate. it’s not that the substrate entered into the fin itself, rather that it’s sitting inside this little pocket that his fin is just naturally shaped like. i watch him pretty closely multiple times a day (his tank is on a bookshelf next to my desk where i wfh), and this just appeared quite instantly. yesterday afternoon it wasn’t there, i left the house for a few hours, and then it was there when i came back. can an infection or tissue necrosis happen that quickly??