Hi and welcome to the forum
Any chance of a picture and short 20 second video of the fish?
If the pictures are too big for the website, set the camera's resolution to its lowest setting and take some more. The lower resolution will make the images smaller and they should fit on this website. Check the pictures on your pc and find a couple that are clear and show the problem, and post them here. Make sure you turn the camera's resolution back up after you have taken the pics otherwise all your pictures will be small.
If the video is too big for this website, post it on YouTube and copy & paste the link here. We can view it at YouTube. If you are using a mobile phone to take the video, have the phone horizontal so the video takes up the entire screen. If you have the phone vertical, you get video in the middle and black on either side.
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How long has the tank been set up for?
How long have you had the fish for?
How old are the fish?
Have you added anything new in the 2 weeks before this started?
How often do you do water changes and how much water do you normally change?
Do you gravel clean the substrate when you do a water change?
What are the ammonia, nitrite and nitrate levels (in numbers)?
