I woke this morning to find a dead flying fox catfish, 1 dead clown loach, 1 clown loach upside down well on its way to dying and another looking real sick, I turned my light on and none of my discus came out when I took a closer look they were all a bit dark and lost their red eyes. I spoke to my sister Karen (Kaza) and she says its probably from me putting a new canister filter in and I didnt know I had to wash it out I just tipped in the round balls in the bottom and switched it on. My worse one is a blue turk which has a sore on his head where it looks like hes scraped it on something but the rest are just dark and sitting in a group in the corner.
I have done a 50% wc added some cycle and a extra airstone. Ive disconnected the canister antil I can fully scrub it and just have the original filter going does anyone know if theres anything else I can do to get them back on the road to recovery I was thinking maybe some stress coat or something like that I hope they dont die thanks guys

Leanne