Tank advice
I have had these fish for around 10 years. They used to live outdoors in a pond but had to move indoors around 2020. The tank is 180L. Most recent move was at the beginning of May, since then it has been a bit of a nightmare.
They used to have a hang on filter which I upgraded to a Fluval 207 just after moving, in the last ~1 month I have had concerns of bad red streaking in their fins and flashing behaviour. I have tried treating with aquarium salts, tri-sulfa & paragone to which none of the treatments have helped with the flashing. The red streaking seems to be improving however.
Initially my water parameters were quite good, 0 ammonia, 0 nitrite and 10-20 nitrates. Since the final dosing of Paragone treatment (2 weeks ago) it seems my levels were all over the place. Ammonia between 0.5-1, 0 nitrate and 0 nitrite. I have been adding Seachem Prime and this week added a few days of Fritz 7 to try and get back to a normal cycle as I was worried all the medication used has destroyed any of my good bacteria in the tank.
You can see in the photos that in the last few days the large silver fish has some tearing of the tail fin which has only just happened. I have unsure if that fish has been going to live even the last few days as has been lethargic, some mornings just sitting at the bottom of the tank.
Open to any advice really I just feel sort of helpless at this point. I live in a small flat currently which is quite old, we have barely any power points and not really any additional space to have a Hospital or Isolation tank if required.