Hello, I have a 20 gallon tank with 5 Julii Cory catfish, 3 kuhli loaches and one betta. Last night I noticed one of my corys was swimming weird and seemed to be floating a bit. This morning when I checked on him he seemed fine but now he is lying on his side at the bottom of the tank not moving very much. After testing the water last night I have 0 ppm ammonia, 0 ppm nitrite and didn’t test nitrate but I did a water change two days ago so I am doubtful that is the issue. Any advice on how to help the little guy would be greatly appreciated.