My cousin is having a problem with her goldfish. He has recently been resting on the gravel in his 2.5 gallon tank. He has also been trying to swim up but keeps sinking over and over again. One day he was accidentally overfed and it was the opposite (he kept trying to swim down but kept floating up). He also is getting a dark spot (like a bruise) near his dorsal fin. To me, this sounds like a swim bladder problem (I had a betta die from something just like this). If I could get some input on what she could do and a diagnosis that would be great!