Urgent help- severe stress and black spot
(had to change the post flair because i couldnt see my own post. thanks UK law)
I've been in tears this morning because I feel like a complete idiot and I'm terrified I might have killed my fish.
Tank size - 374 litres (98 gallons)
Occupants- 2 oranda goldfish
Filtration - aqumanta 200, inbuilt overhead filtration and 2 large sponge filters.
Water parameters- ammonia 0, nitrite 0, nitrate 5-10, ph 7.8 (a 90% water change was done less than 24 hours ago)
Context-
I've had my calico goldfish coming up on 8 years, he's my absolute baby and I've treasured him. He's had his issues over the years but never anything like this.
His tank mate of 7 years passed away late last year, and I'd been reluctant to get a new fish. But I decided late last month that I would get one, as I thought he'd probably appreciate not being alone anymore.
The new fish arrived from an online retailer that I'd never purchased from before, she was kept in an 80L tub for a week to monitor her behaviour, she was active and very healthy to the eye (or so i thought) and I know she should have been quarantined longer especially knowing what I know now, but after a continuous ammonia spike in her tub that I could not shake no matter how many water changes I did, I moved her into the main tank.
They were both absolutely fine, happy as days swimming around together. Up until 4 days ago, when I noticed my older fish bottom sitting with tightly clamped fins. He does it when he's pooping at times, so I thought nothing of it at first, but it seemed to get progressively worse and after a day I noticed it was very clear stress.
Me being an idiot, I thought it may be an internal infection, as he had a small sore on his side a few weeks back (cleared up dosing melafix over the course of a week) and i worried while it may have healed externally, something could be going on internally. So I dosed NT labs internal anti bacterial medication, then did a water change 48 hours later (yesterday)
But I think i was wrong in that.
To cut a lot of rambling, I missed what appears to be black spot flukes on my new goldfish. She arrived with a couple of black spots, but having had a calico fish, I thought it was fading colouration and didn't think anything of it. Looking at the new fish, she seems to have developed more spots, but her behaviour is brighter than my older fish. She's still swimming about, albeit not as much, and is still seeking food.
Im running on the assumption that my older fish had picked up the flukes and I feel so guilty and angry at myself. Please don't come at me for not quarantining the new fish for longer, I'm well aware and if I lose my calico boy I'll be regretting it for the rest of my life.
I do have fluke-solve as a back up, but I am not putting anything in this tank through fear of causing more stress. There's no point in moving him as both fish most likely need treating for the same thing. So im at a complete loss as to what to do.
Pic one is of the NEW goldfish and her black spots. The second pic is my OLD calico, he's upright in this picture, but if he's so much as spooked he panics and tilts to the side after flashing around.
To add- my new goldfishes scales aren't raised, it's just her colouration. It's spooked me a couple of times but from the top view her body is completely smooth.