They prefer one.
Yes, goldfish are very messy. Goldfish need 10 gallons per fish, you actually need a 20 gallon tank or about a 70 liter tank for 2 goldfish. But the small tank will do while they are small, you will need to eventually get a larger tank.
Goldfish do not need their tank light on for more than 6 hours. Unless you have a lot of live plants in your tank, leaving the light on for a long time will result in an increase in algae in your tank. If you begin to see an algae bloom, then you're best to leave the light off for several days.
Either a tank or pond of at least 30 gallons is a suitable environment for a goldfish.
No, in fact they do not need more than 6 to 8 hours worth of light from their tank hood as they should already get natural light during the day.
Regardless of the type or size of goldfish the minimum acceptable size of an aquarium for a goldfish is 30 gallons. Buy a tank that is at least 30 gallons if you plan to have goldfish. You can comfortably fit 3 goldfish in a tank this size but no goldfish in a tank any smaller. Goldfish are essentially pond fish and need lots of space to swim; they will not thrive in a small aquarium.
Goldfish and turtles have different care requirements. Goldfish need a tank with a filter and regular water changes, while turtles need a tank with a basking area, UV light, and a varied diet including vegetables and live food. Goldfish are cold-blooded and need cooler water, while turtles are ectothermic and need a heat source to regulate their body temperature.
Yes, but your tank size needs to support it. If you mean that a regular goldfish is a long single-tail goldfish, then you need at least a 40 gallon tank just for the 2 fish due to the size potential of the common goldfish. If you mean a regular goldfish as in a round bodied fantail, or perhaps a ryukin, then you need at least a 30 gallon tank for the 2 fish.
Goldfish just need a plain bowl and some plants
Yes, the bigger tank the better. They actually HATE goldfish bowls. (they're not nearly big enough). Goldfish usually need a 20 to 30 gallon tank
Depending on what your sick goldfish has, it will either be specific to that fish, which you should place in a separate tank to treat, or it's something that will spread to other fish in your tank, in which case you will need to treat them all.
Lights are important when keeping fish. If you have a goldfish aquarium lighting is important to ensure goldfish keep there Colour. Most goldfish when small may have black or brown spots which will soon disappear wen they grow if lighting is good in your tank. It's also important if your keeping plants real plants need light to establish you can get uv lighting for plant growth
HOPE THIS IS HELPFUL