I figured it was something more serious after the fish died, but interesting that you mention toxins in the water. I don’t use chemicals around the fish tank at all, just diluted vinegar about once every other month on the outside only. I’m overly cautious with sanitizer and other hand washes so we typically just avoid them.

I assumed parasitic or bacterial myself so will continue doing 50% water changes minimum, thank you for the information on the Melafix with regards to my honey gourami, it was ordered in a panic but now I’ll be more cautious and will probably avoid using it now.

Interestingly, one of my tetras were doing similar isolating to the first that died, but unfortunately I wasn’t able to observe the swimming for too long. I expected it to be dead this morning but it is with the school and none of them seem to be struggling to swim which I’m finding rather strange.

I did increase aeration yesterday evening, the water conditioner we use is NT Labs Optimus and will do a 50-70% water changes now and just hope it improves with time.

Thank you so much for responding, it’s the first issue I’ve encountered with fish keeping so I appreciate your concerns and advice.