The Balloon Molly is an attractive, easy to care for fish that thrives in an aquarium with live plants. Mollies are shoaling fish, meaning that they prefer living together rather than alone, which may make your tank feel more alive while also supporting their health and well being. How many should be kept together depends on both their size and needs.
An ideal tank size for mollies is 30 gallons (114 litres, 25 imperial gallons). Anything smaller would not provide them with enough space in their natural habitat - rivers and streams in which there's ample swimming room. A cramped environment causes stress while weakening immunity - while they require hiding spaces to feel secure in their ideal surroundings.
As with most tropical fish, mollies can benefit from having some salt added to their tank water. A teaspoon per 5 gallons will help them retain moisture and avoid dehydration; additionally they prefer an slightly higher pH level of around 7. If you are planning on breeding your molly, set up a separate breeding tank as female mollies store sperm before gestating; you can check her abdomen for swelling or check near her anal fin for dark spots to determine pregnancy. Once she gives birth it is important that the female is removed from her main tank as male adults can cannibalize her fry.