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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What is the ammonia, nitrite, nitrate and pH of the tank water (in numbers)?
If you don't have test kits, take a glass full of tank water to the local pet shop and ask them to test it for you. Write the results down in numbers when they do the test and post them here.
How long has the tank been set up for?
What are the tank dimensions (length x width x height)?
How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
What sort of filter do you have?
How often and how do you clean the filter?
What other fish are in the tank?
How many Pictus catfish do you have?
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Pictus are schooling fish that do best in groups. However, they can reach 8 inches long so need a big tank. Fish swimming back and forth along the glass are usually stressed and bored. If you only have 1 Pictus and the tank is big enough and has suitable tank mates, you could look at getting more, but don't add any new fish until we get this sorted. Pictus catfish are predators and will eat small fish.