Ok so I have a 40gal breeder, I have 2 filters a 10-20 ad 30-40. All 40 gal gets cycled 4-5 times per hour. I have one rainbow shark, dwarf chilild ( not agrissive at all surprisingly.) 3 Molly's, 2 sword tails, a snail, 2 tiger bards, 2 tetras, 2 plecos, 1 platy, and a shark. (Can't remember the name, he has stripes and big eyes like Blackmore goldfish) and a pictus catfish, along with one more catfish. Those are still living I did have 2 balas one was new another 5 months in my tank and a dragon eel. They died all the same day. Now this tank is cycled iv had it around 7 months. I have battled a fungus on a molly I had and now battling it again on my pitcus. My water is good. Nitrates and ammonias are in a really safe range. Water is hard not very hard tho. PH is around 6.8-7. I have a skull and 2 logs for fish to hide along with some fake plants. Also have a peace of drift wood. Water temp stays around 74-76. I do weekly 10 gal water changes i do sifen the gravel and Use prime to remove chlorine and stuff. An I use api stress coat plus. Now I now my fish did not die from using melafix. They died befor treatment and them diein made be see my pictus has a rash. Iv been doing everything right I don't understand why they died. Can anyone help shed some light on the matter. Thank you for your response in advance. Millerchamp.