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We have two small fish in our tank, they seemed very happy until about a week ago. They both became fairly inactive and had their dorsal fins clamped down against their backs. We thought it might be the filter in need of a change so we replaced the cartridge and things started to look up for the gold one, but the black one is still looking quite bad. He spends a lot of time either at the very top or the very bottom of the tank.

Some Info:

  • They're in a 25 litre tank
  • They're both about 5-6cm long
  • There are two plants in there and one piece of wood for hiding in
  • A partial water change is done every week (changing 20%-30%). When the water is changed the glass and wood is cleaned too
  • They last had a water change exactly a week ago
  • We've had them about 2 months
  • The water has been tested at the local pet shop (Pets at Home) and everything was good
  • There is no water heater in the tank
  • After worrying about the filter (it was just a cheap one that came with the tank) it has been replaced with a new one. I read online that this can result in loosing the "good bacteria" so I left the old one in there too (switched off).
  • They get fed every other day
  • The pet shop recommended adding some aquarium salt so I added one tablespoon (as recommended on the packet) a few days ago. This seemed to help for a short while

Any ideas what we could do to help?

The Fish with its fins clamped down

  • I have an idea, but here are some questions... When you say you did a water change, do you mean a partial water change or a full water change? How often have you been changing the water? You say that it started about a week ago, and you also changed the water a week ago. Did this start before or after the water change? – General Nuisance Sep 28 '15 at 0:41
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    By a water change I mean a partial water change (somewhere around 20%-30%). These are done every week and, while I'm doing it I clean the glass and the wood in the tank. It all started before the water change. The fish sadly died the other day but I am still intrigued to find an answer for others and future reference for myself. The other fish still seems absolutely fine. – Phil Sep 28 '15 at 11:33
  • I have seen this a lot with goldfish. Are you using a water heater? – Dupree3 Sep 30 '15 at 19:55
  • Nope, no water heater. I can't say (in my very short time as a goldfish keeper) I've ever seen goldfish with a water heater. – Phil Oct 1 '15 at 10:28
  • @Phil Alright, just wondering. Sometimes with the changing of temperature in the surroundings you can throw any kind of fish off balance. Having the heater would just maintain a steady temperature is all. I had a goldfish that had his fins like that for at least a year before he passed. – Dupree3 Oct 1 '15 at 12:21
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If you got the fish fairly recently, the most likely answer is that they were in poor health already when you got them from the store. This is a very common issue and not all pet stores treat their merchandise the best. There can also be pre-existing issues from where they were bred/raised before being transported to the store, and the transportation itself can be an issue, too.

Hanging out at the bottom, top, the general lethargy you mention, and fins not being displayed are all the fish's way of saying he doesn't feel very well. With the fins clamped, I almost wonder if there was an issue with Itch (did he seem to scratch himself at all)?

They're pretty goldfish, but everywhere I've seen fish, the goldfish always have the worst conditions as many fish are sold as "feeder fish" for other creatures. Your high-res photo was great but didn't reveal any clues.

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    I did wonder whether the fish was ill when it was bought but it seems odd that it took a couple of months to show any signs (would that be normal?). I came across Itch online and I thought it was the most likely cause but I couldn't see any of the white dots on the fish and he didn't seem to scratch himself at all. Whatever was wrong I think the other fish in the tank has fought it off. I'm used to debugging code, debugging fish is much harder!! – Phil Oct 1 '15 at 10:34

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