Frequently Asked Questions
Why is one balloon molly (among others) always swimming at the top?
When one particular balloon molly always swims at the very top of the tank, it is usually a sign of ==swim bladder disorder, a localized gill illness, or bullying==. While it is normal for mollies to naturally graze or “surf” along the surface for biofilm and food, a single fish remaining there permanently indicates a problem if the other mollies are exploring the middle and lower parts of the tank
Because balloon mollies are selectively bred for their short, rounded bodies, their internal organs are tightly compressed, making them exceptionally prone to digestive and buoyancy issues
Potential Causes
-
Swim Bladder Disorder (Positive Buoyancy): The compressed spine of balloon mollies easily pinches the swim bladder organ. If the fish is constipated from overeating or gulping too much air at the surface during feeding, it can become stuck floating at the top.
-
Gill Parasites or Infection: If the tank’s oxygen and water parameters are perfect, but only one fish is acting out, that specific molly likely has a localized gill issue, such as gill flukes or a bacterial infection. It swims to the surface because that is where the highest concentration of oxygen is, trying to compensate for its damaged gills
-
Stress and Bullying: A weak, sick, or submissive molly may be chased out of lower territories by dominant tank mates. It will hover in a top corner or near the filter intake where other fish generally leave it alone.
Troubleshooting Checklist
To determine exactly what is wrong, closely observe the fish and answer these questions:
- Is it struggling to swim down? If it actively tries to swim downward but floats right back up like a cork, it is a swim bladder issue.
- Is it gasping or breathing rapidly? If its mouth is constantly gulping water at the surface and its gills are moving rapidly, it is experiencing respiratory distress from an infection or toxic water.
- Are its fins clamped tightly against its body? This is a universal sign of a highly stressed or sick fish.
- Are the other mollies chasing it? Watch carefully during feeding times to see if it is being bullied away from food
Immediate Steps to Take
- Test the Water Parameters: Use a liquid test kit to check for ammonia, nitrites, and nitrates. Even if only one fish shows symptoms, it could just be the most sensitive individual in the tank
- Fast the Fish for 2–3 Days: If it is a buoyancy/swim bladder issue caused by constipation, stop feeding the tank entirely for a few days. This allows their digestive tracts to clear out
- Feed Thawed, Peeled Green Peas: After the fast, feed the mollies a boiled, peeled, and finely chopped green pea. This acts as a natural laxative for fish to clear any internal blockages.
- Increase Surface Agitation: Ensure your filter or an air stone is creating plenty of ripples on the water’s surface to maximize oxygenation just in case it is a breathing issue
To help narrow this down and give you the best treatment steps, tell us:
- Does the molly float back up like a balloon when it tries to swim down?
- How long has your aquarium been set up, and do you know your current ammonia/nitrite levels?
- Are you noticing any other physical signs like bloating, white spots, or clamped fins?
Any questions? Join our telegram group http://t.me/singaporefish to ask our group experts.