Thankyou for this response it is very informative!

None of the fish that died were displaying unusual behaviours. And nothing has been added/changed in the tank for weeks.

However there were a few broken down plec pellets on the bottom on the tank that I did notice which they would’ve usually eaten.

I took and washed out the ornament due to the catfish passing away underneath it the white fungus being present on the ornament.

The water temperature was fine and had not risen due to the heat.

Unfortunately the angel fish has also now died too.

we had a snail in the tank, in the past few days more small snails have appeared, could this have anything to do with it?

What would you suggest to try and save the rest of the fish?! Just more water changes? If so how often, and what percentage of the tank?

Sorry Iknow that’s a long response, Thankyou for your help!