We need pictures of the dead fish and any remaining catfish. Also a picture showing the entire tank.
Test the water for ammonia, nitrite, nitrate and pH. Post the results in numbers here.
What are the tank dimensions (length x width x height)?
How long has the tank been set up?
How long have you had the fish for?
Did you add anything in the 2 weeks before this started?
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?
Do you dechlorinate the new water before adding it to the tank?
What sort of filter is on the tank?
How often and how do you clean the filter?
What is the
GH (general hardness),
KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg:
ppm, dGH, or something else).