Could someone help me figure out why my guppy spends most of her time at the surface of the water? She puts her mouth at the surface as if trying to get more oxygen. But I don’t think oxygen deficiency is the problem. The tank is well aerated with an air stone. All the parameters are good: ammonia 0, nitrite 0, nitrate less than 40. An inspection of her body doesn’t show any signs of illness. I noticed this behavior about one or two months ago when she had a male guppy companion who died. I’m not sure if loneliness has something to do with it? It’s a 10 gallon tank with two black skirt tetras, one betta, and one glolight tetra.