MDr Huw Stacey, vet and director of clinical services at Vets4Pets, is here to answer all of your pet problems. y son’s goldfish, who’s Sadly, it sounds like your fish is not well, either through about three years old, an infection or internal problem – but possibly due to the has been sitting on the water quality and filtration and oxygenation system. Get bottom of the tank an aquarium test kit and check the water for pH, nitrates, breathing heavily for the ammonia, chlorine and hardness. Also check that your last few days. What can we filter and oxygenation system work properly. Changing do for it? one-third of the water and trying tonic salt for a few days may help. If the fish has signs of parasites or infection your aquatics centre can supply a treatment product.