How to Take Care of Goldfish?

1.Get a large enough tank. The minimal tank size for one goldfish is 10 US gallons (Remember, they grow to about 10-12 inches, and sometimes over!) and you will need to add 10 US gallons onto that for each additional goldfish.
-->For example, one goldfish needs 10 gallons, two goldfish need 20 gallons, four need 40 gallons and soon and so forth.
-->As babies, you can provide them with a five gallon tank, but you'll want to upgrade to a bigger tank size very soon.

2.Use gravel that won't get stuck in your fish's throat. Use either large rocks (too big to swallow) or very small gravel. Large gravel is better for goldfish because it won't get caught in their throat and because goldfish like to be able to dig into the gravel to search for fallen food.
-->Be sure to clean your gravel before you put it into the tank. Even if you've bought it new, a good rinse and soak in some water for a day will draw out some of the impurities and help ensure that your goldfish are getting the best possible environment to flourish in.

3.Make sure your tank has some scenery and light. If your tank has gravel and nothing else in it, your poor goldfish won't be very happy. Goldfish also like light. Try to keep your aquarium lit for 12 hours each day.
-->Think about putting a rock or wood centerpiece with some artificial greenery into your aquarium. The rock or wood will give the goldfish nooks and crannies to explore and the artificial plants won't accelerate plant growth in your tank.
-->On the other hand, real plants are beneficial because they help absorb some of the ammonia, nitrites and nitrates that accumulates in the aquarium because of waste and natural wear and tear.
-->Be sure that any decorations you choose aren't hollow (it's a breeding ground for potentially harmful bacteria) and that they don't have sharp edges (your fish might tear its fins).
-->Try using fluorescent lights for your goldfish. Halogen lights and incandescent lights will also do. Pay attention to how much light you give them — goldfish love light.
4.Rig up a water filter. A water filter should take care of the breaking down of the fish’s waste by beneficial bacteria; the trapping of larger particles such as fish waste or excess fish food; and the removal of odors, discolorations and other organics by carbon or mineral absorption. Having clean water and a functional, efficient filtration device will keep your goldfish content and healthy. There are three very popular kinds of filters:

-->Hang on back (HOB) filters, which hang on the rim of your tank, and bring water in and filter water out. They are very popular, reasonably priced, and probably give you the most bang for your buck.

-->Canister filters sit underneath your aquarium and use a series of tubes to filter water in and out. Canister filters tend to be almost silent, are a little pricier than HOB filters, but tend to be more efficient at filtering than HOBs.

-->Wet/Dry filters use an overflow box to filter out impurities. Wet/Dry filters, however, are significantly bigger than HOBs or canisters, and so generally only fit into aquariums that hold at least 50 gallons.

5.Go through at least one fish-less cycle before introducing your goldfish. A fish-less cycle involves adding ammonia to a tank and keeping track of the nitrate levels to make sure the water is safe for your goldfish to live in. Sadly, many fish die once introduced into a new tank because of ammonia and nitrate poisoning.

Next 4 Steps are:

1.Perform a 10%-25% water change weekly assuming you have one goldfish per 10 gallons. If you do not have a filter in your tank, do a water change twice a week.

2.Clean the aquarium at least once every two weeks. Goldfish produce waste that even your water filter won't be able to zap. A clean tank means happy, healthy goldfish.
-->Do not remove the fish from the tank when you clean. Using a gravel vacuum to soak up debris can be done without extracting the fish from their habitat. If you have to remove the fish, for whatever reason, use a plastic container instead of a net, if possible. Nets can injure goldfish fins easier than containers can. If you need to use a net, soak it before capturing the fish.
-->Measure for ammonia, nitrite, and pH. Ammonia and nitrite levels should be at 0. A range of pH 6.5-8.25 is fine.
-->Soap is poisonous to fish and will kill them quickly, so don't wash your tank with soap. Also, don't use regular tap water to put in your tank. Drinkable water is not good for them because it takes out some of the minerals which are good for goldfish. Buy a water conditioner at a pet store and put in the amount it says on the label.
3.Feed your fish 1-3 times daily. Be careful not to overfeed them, and always follow instructions on the label of your goldfish food. Goldfish can easily overeat and can die. Underfeeding is always preferable to overfeeding.
-->Just like humans, goldfish want diversity of nutrition. Feed your goldfish flake or pellet food most of the time, live foods, such as brine shrimp, some of the time, and freeze-dried foods, such as mosquito larvae or blood worms, every once in a while.
-->Feed your fish only what they can eat in five minutes. Remove any excess food. More goldfish die from overeating than from anything else.
-->Feed your goldfish at the same time each day (once in the morning, once at night) and in the same spot in the tank.
4.Let the water temperature change as the seasons change. Goldfish don't like temperatures over 75°F (24°C), but they appear to like seasonal changes where the temperature dips to the high 50s or 60s (15-20°C) in the winter. Understand that goldfish will not eat below 50-55°F (10-14°C).