Hi all. in the last week I had two of my large angel fish die. They seemed to be healthy and then they started to float with the mouth up and their tail down near the surface. they didn't really move much and then the next day I found them dead. They didn't have any spots on them or look of a parasite. I have a 20 gal
long with some loaches, 2 catfish, 1 algae eater, and another small white angel fish.
Now my small white angel fish is doing the same thing. All the other fish are fine. any ideas what is wrong?
I have a undergravel filter and my tank has been set up for about 6 months. I do a water and gravel vacume at least once a month sometimes more.
I live in Hawaii so I don't have a heater in my tank but it has been colder and I wonder if this could have affected my fish. Any ideas? Thanks.