goby dying

He lost his strength and won’t move or eat. I had him for about a week. I have a 10 gallon tank and do 30 percent water change every week. I don’t know what is did is wrong… he looks happy and fine two days ago.

Our diamond goby has been acting weird the past couple of days. We have had him for about 8 months and he has grown a ton but seems to be short of breath and less active in the last couple of days. Last night he seemed 'frozen' at a part of the tank he is not usually in, mouth wide open, not...