Do rounded or half-moon fish tanks harm my fish or distort vision?

It's not really recommended to keep fish in bowls with no filtration. And 2.5 gallons isn't really big enough for much. A Beta fish may possibly do ok in it if you can maintain it. But I would recommend more doing plants and a few snails or ghost shrimp type of animals in a bowl that size.

Hi, and thanks for your question. There is a general rule about it which is a rough estimate not to overcrowd your aquarium and avoid excessive production of feces and organic debris. The rule is one Inch per gallon, so in 10 gallons there should be ideally 10 inches of fishes in total. You should consider as well the presence of plants and gravel and any other sort of things, which decrease the water volume of 5-10% (so 10 liters are actually 9-9.5). This rule does not consider modern filtration systems. These fish suffer genetically from a certain grade of visual impairment, so overcrowding (especially competition for food) is not recommended. At the same time, please consider as well that schooling fish (like they are) should be kept in numbers, which means more space will be needed, so be generous.

Hi I don't recommend using distilled water in your tank as the "osmolarity" of the water can cause problems for your fish. Either pick up a bottle of water conditioner from a pet store or draw a large bucket of tap water and let it sit for 4 or 5 days. Some of the chemicals will evaporate out when left to sit, but it's not such an ideal option.

Without anything to use for scale, it is hard for me to tell how big your tank is, but in general it seems very small. Also, the water that is in the tank appears very cloudy right now, so that would be the first place to start. Water quality is very important, and will make or break your ability to house and care for fish. I would recommend getting a good filter system (you can visit a local pet store to assist you with brands in your area, as I am not familiar with what you can get in India). Be sure to bring the measurements (height, length, width) of your tank, or the gallons or liters so they can tell you what capacity of filter you will need. Everything else will depend on what types of fish you get - if you plan on getting multiple fish, they will need to be small - a general rule of thumb is one square inch of fish per gallon of water. Depending on the species you get, you may need to also get a bubbler to ensure there is enough oxygen in the water for them, and you will also likely need to get some sort of substrate for the bottom and cage furniture (different species have different air requirements, and some are secretive and like to hide). You may also need a water heater, depending on the species you would like to house. But, depending on how small your tank is, it may be hard to get a water heater that will fit. The food type will also depend on what species you get, as there can be differences in diet type between species. I hope that gives you a place to start, and good luck!

As for what kind of tank you will need: Basically a square fish tank, do not get a bowl. You will likely need a heater and an air pump, and a thermometer, It is easiest to by a complete kit at a pet shop. As for size of tank: The bigger is always the better....however a minimum size will be determined by the type of fish and their average size they will grow into, So once we know what type of fish you have and how many, we can tell you how big your tank needs to be and what type of "furniture" (rocks, plants, gravel) you will need.

It could be an infection or tumor. An infection may be resolved with proper treatment but you would need to get Rory and the other fish out of that small bowl. It is much too small for one goldfish, let alone three. Goldfish need large tanks because they produce larger than normal amounts of waste. Ideally, 1 goldfish should have a 20 gallon tank. Add an additional 10 gallons per extra fish. That would mean you need at least a 40 gallon tank. You also need a filter in there. The filter should be rated for at least twice the volume of the tank. To keep them in a small bowl will drastically shorten their lifespan and could lead to stress and illnesses.

RO water is devoid of minerals and trace elements that help stabilize pH and other parameters. If you can add these after filtration then use your RO water. Otherwise, RO is commonly used to "top off" fish tanks that lose water via evaporation.