Hiya, so I’m new to this forum and owning an aquarium. I purchased a rectangular 60 litre tank with a filter, heater, air pump etc for tropical fish. Everything was washed before being placed in the tank with warm water. I also got some aqua start and bacto start for the tank because it was new and I read that this would help for the new fish. I let it cycle through. I then I purchased some 6 X cherry barbs and 2 X zebra snails. After letting the bag sit in the water for half an hour and letting water into the bag every 10 minutes or so I let the barbs out of the bag and the snails. Everything was fine for around 8 hours until the water started going milky, which when I checked google it was called “bacterial bloom” and should be expected when putting new fish in a new tank. About 4 hours later the fish one by one started to rush to the surface and gulp the air, shortly after that they would go lifeless and float around the tank and then suddenly come back and then go lifeless again. Then I’d find them dead at the bottom of the tank. I’m not sure what I did or how I can fix it. Could someone help me?