Fantail sick....

[Tatianna]

Hello, I need some help with my fantail PLEASE! This fish has had problems for the past month maybe month and a half. First off, my daughter was gifted this fish about 3 years ago by one of her oncology nurses. Until recently we haven't really had any issues with 'him'. He is alone in a roughly 58 L tank. Around 4 to possibly 6 weeks ago he started getting lethargic and laying on the bottom of the tank....he has always done this a little, but it started to become constant. I checked the water and it was fine, ph was a little high, but within the normal range for this tank. I did a water change as per usual for tank maintenance. A few days later one of my kids noticed the top part of his tail was gone....just gone. I thought maybe he had torn it on a decoration, so I took out the decoration in question and vacuumed the rocks to see if I could find the missing fin. Nada. So I start looking at him a little closer, but I don''t see any white area around the fin to indicate fin rot. By this time the fish is sinking to the bottom like a rock if he stops swimming and it seems like he can't even make it to the surface of the water without swimming really hard. I do another partial water change this time about 50%. We to into our local fish store and the owner recommends salting the water. I already had aquarium salt so I add this when we get home. Still no improvement after a few days. Dear hubby is convinced it is fin rot so we go buy a 5-in-1 treatment (all we can get locally). So we follow the instructions on the packaging and the fish seems to improve. However after the 6th day now the fish seems to be unable to stay below the surface of the water and he rises up if he stops swimming! We check the water and find some ammonia, so we do a 50% water change and add cycle as if setting up a new tank thinking the meds wiped out the good bacteria. We do 2 more 25% water changes and once again the fish is sinking to the bottom and lethargic. hardly moving and I am seriously worried this fish is dying! We try a new 'pet'store in town, but the workers really don't know anything....the suggested we try something for a possible parasite....and that is where we are now. I don't know what else to do. This treatment says to put a dose in wait 48 hours add a second dose. Tomorrow will be the first 48 hours....Please help. We don't know what else to do!