Golden Denison barbs not doing well

Hi. I have 4 golden Denison barbs in my aquarium. Added them about 3 months ago. All of it were very active and brightly coloured. This morning I noticed one of my barb was not very active, stayed down in the aquarium, trying to hide behind my plants, and not swimming around like how it used to. And I also realise the colour of my barb have lightly faded, looks pale. It doesn't look swollen and no visible wound or infection. What can be the issue? Do I need to quarantine it in a separate tank. I really hope I can save it.

Can you give the aquarium size, maintenance routine and water chemistry results plus a photo of the aquarium and affected fish please as that will help sort what might be wrong

Thank you

wasmewasntit said:

Can you give the aquarium size, maintenance routine and water chemistry results plus a photo of the aquarium and affected fish please as that will help sort what might be wrong

Thank you

Click to expand...

Aquarium size is 60 × 30 × 36 in cm.
Weekly 40% water change and cleaning of filter. I have currently kept the fish separately, I am not sure if it's a disease, afraid that It might spread to other fish.

First thing that leaps at me is that your aquarium is too small for Denisons, they are long distance swimmers and really need a minimum 55 gallons to stay healthy

The aquarium is very overstocked with the Denisons, Glofish and Neons. That will cause issues with water chemistry due to excessive waste production

Cleaning the filter weekly is not required...the floss should be changed weekly but the rest of your media should stay put til it literally falls apart before changing, noodles or ceramics should stay put and only be lightly rinsed in aquarium water during water change once every few months. With your current overstock you should fo 50% water changes two or three times a week.

Test strips are notoriously inaccurate, which with your stocking overload, you would be advised to buy a liquid tester kit which are easier to read and manage

Next step from here would be to return the Denisons to the shop they were purchased due to being unsuitable for the aquarium size. Then you could really do with deciding either Neons or Glofish but probably not both in what looks like a 60 litre aquarium. Unless you reduce the load your water chemistry will never balance.

Did you fully cycle the aquarium before adding fish?

@Byron
@itiwhetu
@WhistlingBadger

I concur with @wasmewasntit post. I will just mention one more problem, and that is numbers of the Denison species. Compatibility/Temperament: Generally peaceful, but should not be kept with smaller fish that will likely be seen as food. It's water flow and cooler temperatures limit suitable tankmates to medium-sized barbs and danios, loaches, Garra and Devario species. Must be kept in a group, minimum 8; reports of aggressive behaviour are likely due to the fish not being maintained in a sizeable group.

It is more than likely that your hiding bab is stressed and being targeted by the others, this will only get worse. This tank is no where near large enough for a group of 8, so it would be best to rehome the three/four ASAP.