I have two apistogramma steindachneri females that I have had in the same tank for over 3 months now. They are in a 10gal, heavily planted aquarium by themselves and one kuhli loach and a couple pest snails that come and go. I have had zero issues with them, until yesterday. I noticed one of the apistos wasn't out and about like it normally is. After searching for awhile I found her hiding in the in some plants in back of the tank hardly moving. I let her be and fed them normally that night and she didn't come out to eat like she normally does. I did eventually see her get a little bit to eat but definitely not as much as normal. This morning she was hiding in the plants again not moving around. I was able to get a net back to where she was and she went in the net with fight. I pulled her to the front so I could look at her. I noticed that one of her gills was very swollen, but I did not see any white or red spots on it and the other gill looked completely normal. It also didn't look like it was injured. She has not been going to the top for oxygen at all. She has just been sitting under plants near the bottom of the tank. The other apisto seem completely fine and normal as well as the kuhli loach. I don't have the numbers on the water parameters but I know that they are all in normal levels and the temp is good. Does anyone have any ideas what could be going on? Thank you so much in advance.