Samantha started to curl on and off since Christmas, after the weekly water change. Normally she's only like it for a couple of days and then straightens back to normal, some water changes haven't affected her at all. Three weeks ago, she curled up on the Tuesday (after I did the water change on the Sunday) and this time she is showing no signs of unbending. I'm not sure how much longer I should wait before putting her to sleep. She has so many health issues, and although she is eating and desperately trying to swim, I can't justify leaving her in her present condition for much longer.
I've tried using salt, which in the past has worked. I added it to the tank and also tried a more intense salt bath. Both have been unsuccessful this time.
It is so difficult to know. I know in the past I have felt with hindsight that I should have acted sooner on euthanasia for elderly sick pets. I think if you are feeling this it is likely to be time soon?
I've been in the situation of my goldfish having a very acute illness and looking like there was no way that he could possibly pull through, and being advised to put him to sleep, only for a further last-ditch attempt with anti-bacterial treatment to completely turn the situation around - and for him to survive another 4+ years.
I've also been in the situation of the same goldfish developing several chronic conditions, then take a dramatic turn for the worse over the course of one particular day, and being advised to put him to sleep, but again unable to do it. In this case, he did die, and I feel bad about how much he probably suffered on the last day (but, equally, would have tortured myself if I'd put him to sleep and always wondered if he might have pulled through as before).
It might be worth imagining yourself in the situation of having put her to sleep. Do you have any regrets or do you feel relieved for her? Are there any medications that you wished you'd tried a last-ditch attempt at, just in case it might have turned the situation around? This might help give you the answer as to what's best to do in this situation. If you are absolutely torn as to what to do, then I'd let nature take its course, whatever direction that goes in.