Hi and welcome to the forum
You need a picture on the back of the tank to make the fish feel more secure. You can buy aquarium backings from pet shops or online, or use a black plastic bin liner or coloured card and just tape it to the outside (on the back) of the tank.
Did you cycle the filter/ tank before adding fish?
Cycling a filter is where you add ammonia and let beneficial bacteria grow in the filter media/ materials. After about 4-6 weeks you add fish.
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Most fish health issues are caused by poor water quality. Below is some info on what to do if the fish ever look unwell or off colour, or aren't acting normally.
BASIC FIRST AID FOR FISH
Test the water for ammonia, nitrite, nitrate and pH. Post the results in numbers here.
Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.
Do a 75% water change and gravel clean the substrate every day for a week or until the problem is identified. The water changes and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.
Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.
Increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.
Post clear pictures and video of the fish so we can check them for diseases.
You can upload videos to YouTube, then copy & paste the link here.
If you use a mobile phone to film the fish, hold the phone horizontally so the footage fills the entire screen and you don't get big black bars on each side.
