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.
- 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 for 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 losing 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?