I was on the Goldfish Paradise forum, but it appears to be gone. This place looks like the most active forum I can find right now, so here I am.
Size of tank: 10 gallon
What filter do you use? 10-15Gal canister filter
How long has the tank been setup? Year and a half
What water tests have you done and what are the readings? Nitrate, 0; Nitrite, 0; Hardness(GH), 75; Alkalinity, 120; pH, 6.8. I don't have any tests for ammonia, and I don't have a thermometer in my tank. It doesn't feel any different than my room temperature, which is around 75; which I believe is around 23-24 centigrade.
When was the last water change and how much did you change? I did a 50% yesterday while vacuuming my gravel.
A list of all the inhabitants? Two comet goldfish.
When did you last add fish, plants, ornaments or other tank equipment? Over a year ago.
Have you added any medication? No.
My fish has been doing backflips in the past few days. At first, I just thought my little dear one was being cute, but then last night I noticed that she [or he, I don't know] was doing a sort of vertical float with her her facing upward.
Today, she has been prone to bursts of inactivity and lethargy. She has also started resting on the tank floor.
Her breathing is rapid and shallow, and within the last hour, she has developed a hole on her gill that looks like it's bleeding.
On closer observation, the fish is swollen behind the gills; the scales are starting to poke out. She also isn't pooping normally- it's just the casing with nothing in it.
I tried to feed her a pea, but she wouldn't touch it.
The other fish in there is perfectly active, very happy.
I don't know what I should do... At this point, should I consider euthanasia? I don't even know how to euthanize a fish. I just don't want her to be hurting anymore.
Looks like an ulcer to me and basically a serious bacterial infection that will need to be treated with a proper anti-biotic like Furan 2. They're all perscription medications in the UK so really you should get the fish to a vet. Many vets are experienced with goldfish as they're so close to koi.
As a side note, it appears you are using a 5in1 dip strip type tester. Not only are these very expensive per test but they're also hugely inaccurate. Get yourself a proper liquid based test kit that will test for Ammonia, nitrite, nitrate and ph properly. API Freshwater kit is a good one.
Another problem you may not have been aware of but the structure of that fish isn't right. He's suffering from lack of excersize and cramped conditions. As soon as possible both fish need to be rehomed to a much larger tank or possibly a pond. They should grow to 12" in length and live for over 20 years. Common goldfish like this really need a tank at least 5' long. (60gallons+)
Looks like an ulcer to me and basically a serious bacterial infection that will need to be treated with a proper anti-biotic like Furan 2. They're all perscription medications in the UK so really you should get the fish to a vet. Many vets are experienced with goldfish as they're so close to koi. (60gallons+)
Shouldn't be a problem for the OP to get Furan2 EC, as she's in the US. Probably worth getting LHG to look at it, though
Sounds like eaglec is on the money, chances are the bacteria has hit at a later date rather than being a problem from introduction given the timescale involved so yourt most likely cause would be aeromonas or furunculosis, something thats opportunistic and almost omnipresent in aquaria, and more likely to occur with fish that are cramped.. Furan 2 will shift that, and yes the goldfish is showing signs of dwarfing and its form isnt too good structurally.The primary reason its getting these infections is not just the presence of the bacteria which would be less pronounced in a larger better oxygenated aquarium with higher flow rates, but because the dwarfed fish typically has a less efficient immuno response.
These are comet goldfish so more appropriate starter tanksizes, (which also make treatment safer) would be 30 gallons, later 55 gals, and for those fish with a big growth potential, even potentially larger later on, perhaps even 75-100 gals for multiple fish, better yet a pond.
The dwarfing the fish is sufferring from will have to be reversed, or this sort of thing will keep on happening and goldies only survive so many doses of meds like furans. Getting him well and out of the risk zone for infection will take treatment now and some immediate redressing of his environmental needs to improve the chances of long term survival. Even powerful filtration does not make up for the volume needs of comet goldfish. They really need the volume no matter what the standard of filtration is. Growth and the avoidance of dwarfing is about fitness, exercise, good gaseous levels, and water quality stability that changes very little vs time, and none of that is acheivable over the long term with fish of this growth potential in small aquaria. Thats why we have a 30 gal minimum for goldfish on this site, and for comets in particular the door must never be closed to even larger tanksizes depending on the growth response you get from the 30 gallon minimum.