I may be posting in the wrong thread. Please correct me if so. Pictures included so you can have a better idea of what's going on (see: the silver mollies and Blue the Platy). For the past month or so my poor tank family has been hit by a number of losses. I am absolutely out of my league and need help. I started my tank months ago with 6 Albino Tiger Barb's and four Platys from a local PetLand. Our only issue after adopting them was an occasional ammonia spike and keeping the water clear. Life was good. One day I notice some of the scales on my favorite Platys chest seem raised. Her name was Blue. I think maybe one of the Tigers took a nip, but she's swimming and eating so I don't think much of it. A few days later I find her dead, the chest 'wound' dramatically worse--it looked like internal bleeding, all this red beneath her chest and belly. It was strange to me because my Barb's are incredibly mellow. We have a sad fish funeral and move on. After a few weeks we go to PetSmart and adopt 10 Neons and 3 Cory's (2 albino, 1 panda). Water perameters stay about the same. Things are a little cloudy sometimes and ammonia goes up every now and then, but none of the fish act sick. A few days pass... The Panda Cory has white stuff covering him head to tailfin. I worry, pour in Melafix and aquarium salts based off some forums here. None of the other Cory's are sick, nor the Neons I purchased with the Panda. Two days later, the Panda dies. We decide to buy a better filter. We get a SunSun 302. Add fish floss and ammocarb to the layers. Tank clears up, water is Crystal. Purchase something to monitor the ammonia, still spikes occasionally but we have it under control and none of the remaining fish act sick. We think the problem is solved. We are very wrong. Over the course of a week and a half we lose our remaining Platys. They stop eating, all of them, and spend their time exclusively at the surface of the tank. They are lethargic, fins appear to be rotting. Occasionally I would find one sitting at the substrate, unmoving save their gills. The last one to go developed some sort of swim bladder issue. She couldn't keep herself up right before she finally kicking the bucket. We use Melafix as directed, and a 50% water change. They all die regardless. At this time, all 11 Teras, 6 Barb's, and 2 Cory's are still behaving as usual and are completely uneffected. We wait a while, test our water. Everything seems okay again. My roommate has a considerably smaller tank. His guppies give birth and he needs to move some of the babies. We wait until theyre a little over a half inch and move them to my tank since I have excess room. They die in two days; in retrospect I believe their tiny fins were rotted and what may have been ich was developing. They were small and it was hard to tell. At the time I thought they died because of how quickly we transitioned them. I am very inexperienced and recognize this was not the case now. Another week passes. Another water test. Everything is perfect, water crystal. There's some algea developing so we a 25% water change and clean all our fake plants and our bubbler. We go out and adopt 4 Silver Mollies (collectively named Karen) and a baby bristlenose Pleco (Taz). This time I am very conscious of the transition period. I spend 40 minutes getting them ready for the tank. I float them for 15 minutes, then spend the rest of the time slowly mixing tank water into their bag. Then I release them. I shut off the lights for 4 hours and add stress coat. I turn the lights back on to see how my new additions are fairing. I'm horrified to find all the Mollis covered in what may be ich. They're eyes have white stuff growing on them, their fins look rotted, and the same white stuff is covering all their fins and patching their bodies. They look like their flesh is fraying. This all happens in the tiny 4 hour span with the lights out. The pleco is perfectly fine, and so are all my other fish. It is very late at night and we panic. We put ammoxicillan in the tank because no stores are open. We expect the worse but hope for the best. The next day, all but one Mollie is dead. There is barely any of the white stuff on the surviving Molly, same as her dead siblings, but she's very lethargic. I fish out her dead siblings and have to leave for the day for work. But I come home with Neoplex. I use as directed. The Molly still looks better but won't eat and is hovering at the substrate. Pleco and all other fish are acting normal. I let the medicine do its job over night and while I'm at work. I came home today to find the remaining Molly and my previously unaffected Pleco dead at the bottom of the tank. Neither are covered in whatever the white stuff was, in fact the pleco looks physically perfect--fins and color. All other fish are acting healthy as usual. What the heck is wrong with my tank. Please help, I am so confused.