Goldfish bleeding and flashing at night.
I was hoping you could help me as I'm at my wit's end. I have two 16 year old goldfish living in a 200 litre tank. The smaller one of the two is very stunted, she is only about 4 inches long (I received them as a child who didn't know any better, and kept them in a 60l tank until I moved out, I'm now trying to make up for a lifetime of bad care). The other is about 6-7 inches and has never presented with any health problems.
For the year or so, I've been seeing the occasional red dot appear on the smaller one's fins, body, and gills, I'm very vigilant about my levels and ammonia has never been an issue. Whenever this happened, I did a 50% water change and used salt which seemed to help. In terms of medication, I am in the UK so it's quite difficult to find stuff that is actually effective. I have tried Interpet anti internal bacteria and anti internal parasite but that always felt like a stab in the dark and didn't do anything to prevent the spots coming back. She always healed within 2-3 days. As a routine, I do 40% water changes once a week, testing right before a water change and then another test halfway through the week.
In the past couple of weeks, she was very red and bleeding around the base of her pectoral fin, in the socket where it connects (first pic). This healed over the course of around a week with only water changes. I woke up this morning and she has a "collar" of wounds/bleeding around her chin. She flashes with irritation, but only at night. Behaviour-wise, she is exactly the same as usual other than the flashing. She eats like a trooper. I have tried praziquantel, the flashing and the fact that the bleeding is around the underside of the gills made me think it was flukes. The wounds themselves, as well as the flashing look really distressing. Could it be her stunting is catching up with her? She behaves quite erratically at food-time as well, and throws herself into the substrate so it could be a mechanical injury? Any help would be appreciated, thanks.