We had a death of a clown loach with mysterious timing and hoped the collective knowledge of the group could help.
we have been keeping fish for approx 5 months now and some of the original stocking and equipment decisions were made by the kids prior to understanding some of the intricacies of community tanks...my bad.
we have a 40L planted tanks with 5 (now 4) clown loach and an angel fish. Yes too small for the fish we have, we have a 400L tank but not set up as we are moving soon and I will do it then. The loach were small when purchased and very active, once the angel was added he asserted himself as the dominant fish, bullying the others into hiding.
A new larger tank was set and the angel fish was moved, slowly the loach went back to their old ways but two days later we found one dead, no external injury but a red mark on his forehead that looked like internal bleeding. Tank conditions had been checked only the day prior and were excellent and no other disease in the tank bar some manageable algae.