Many aquarium fish are susceptible to fungal, bacterial infections. 

Also the most common issues that fish tend to get is "bladder paralysis" and  "intestinal bloating" .

We often see an improvement if diet is changed.  E.g. better quality dry pellets or flakes.  Even some live warms can cause bloat in gold fish. These are some of the thing to look out for if you fish tend to die from bloat or float and swimming issues.

Use the hampls "fish bloat" natural (homeopathic drops) for treatment or prevention.  And has this formula is all natural, it will not hurt of affect other fish or the water.

Easy Dosing:   the most effective and fast relief that I have found, is to pour a capful of the formula onto the affected fish when they are up feeding, or when floating on surface, this way he or she is getting a direct dose on body.  Even if you have to use a net to bring them up close to the top to dose the formula over him. Depending on how bad he is, give 3 doses each repeat dose is 10 to 15 mins apart.   Otherwise a casual dose twice a day if swimming difficulties or not acting normal swimming with other fish.

For general infection, virus bacterial prevention or relief, we like to suggest the colloidal silver of a tablespoon for say a 60 gallon of water tank.  Less for smaller bowls or tanks.  Repeat once a week for as long as needed.