As an extreme measure, since fish are dropping fast, it might be worth at least thinking about removing and euthanising any fish that are showing symptoms, like the ones in the photo. Whatever this is, it's pretty brutal and spreading fast. We don't want the other fish to pick it and eat the bodies, as fish normally do, since this only means ingesting more of the pathogen from fish that were definitely infected. It's an extreme measure and not a nice one to think about, let alone do, but it could mean the difference between saving some, or losing the whole tank. Clove oil is a humane and peaceful way to send the fish to sleep before overdosing them on clove oil so they pass in their sleep. I've done that method for fish that were dying and suffering, so they didn't have to suffer in pain and linger for days before dying. Can talk you through how to do that method if you need it, and there are youtube tutorials.
For small fish like the ones you have, there's also the old school method of putting the fish inside some folded paper towel and hitting hard with a heavy book or similar, for instant death, but not everyone can face that method either. It is at least quick, which can be more humane in some circumstances.
Another option is to set up a bucket or container with an airstone and a heater (ideally with heater guard) and move the obviously sick and any dying fish to that, to isolate them from the others and make sure the bodies aren't eaten.
For future use, some people have a spare tank always set up for quarantine, or one stored away to use when needed. Depends on what you want and need for your own set up. If you're not bringing in new fish often, and you have small species of fish so don't need to store a large tank, a ten gallon tank is fine for quarantine use. Just needs a simple sponge filter, a heater, some spare substrate since bare bottom tanks can stress fish out, and some decor of some kind for the fish to hide away and feel secure. Plastic plants can be washed and steralised in a bleach solution after use, especially if the fish did have any disease or parasites, then stored away when you don't need the tank set up. I favour fake decor for the quarantine since it can be cleaned/bleached, unlike wood or stone.
You can also use a plastic storage tub like this:
as a temporary or emergency quarantine container, provided it hasn't been used for anything else but fish stuff, so get a new one if you plan to try this method, and only use it as a quarantine/fish keeping storage box in between uses. Using a storage box you have already isn't a good idea since any chemicals from things it might have stored, like fabric softener from clothing or things like perfume, air freshener or cleaning products can leave a residue on the plastic and poison the fish otherwise.
I didn't have a heater guard when I used one, so I carefully placed some stones to rest the heater on and keep it well away from the plastic. A heater guard would be much safer. But this plastic storage temporary tank is useful when you're in a hurry or don't have space to store a space tank. I keep an extra sponge filter running on one of my main tanks, so it already has BB and I can move it from the main tank to the QT as soon as I need it, and it'll already be primed to cycle the QT. I also add trimmings from plants in my main tanks, only the plants I don't mind binning after quarantine in case there is a disease or worm eggs, I don't like moving any plants from QT back to my main tank just in case they're contaminated, and medications often kill plants anyway. You can also buy bunches of elodea or hornwort and throw those in. They're inexpensive, fast growing so help with water quality, and give the fish something to hide in and a sense of safety since there's something floating near the surface they can hide under.
Why are fish medications banned in the uk?
They're not banned as such, but antibiotic fish meds are tightly regulated because of antibiotic resistance. People have overused and misused antibiotics so much, that people are dying from illnesses that might have been curable with antibiotics, but the antibiotics are now less effective. We can only get proper antibiotic fish meds like the ones available elsewhere through a vet's prescription, and not many people want to find and pay for a vet that has specialised aquatic experience, for the sake of a £2-3 fish. But might well do if they have expensive fish.
But standard antifungals, methylene blue, wormers etc are all available. As
@Essjay said there are a couple that at least have an antibiotic effect like the eSHa-2000, but they're not as strong/effective as the meds available in the states.
So thank you for that, it's always nice when people return to let us know how things turned out. It's so often a mystery and we just have to hope for the best.
