Now that you have everything in place, you can add in the water. You will need to use a dechlorinator, as the chlorine in tap water is poisonous to fish. Once the fish tank is filled up, you can turn on the filter. Change it as often as recommended to keep your fish healthy. Goldfish live at room temperature, so you will not need a heater. They are quite comfortable in temperatures from 68 to 80 degrees. However, they should not be exposed to rapid temperature changes. You might want to let the filter run in the new goldfish tank for a day or so to filter out any chemicals or dyes that might have been left on the gravel and decorations that you just added. Waiting to buy new fish can be one of the hardest things about fish keeping!
You need to add fish gradually. Fish excrete ammonia. If you add too many fish at once to a new fish tank, the water will not be seasoned enough to dissipate it. As the water in your Goldfish tank ages, it builds up beneficial bacteria that turn harmful chemicals excreted by the fish into harmless ones. However, this will take some time. Start out with only one fish. The nitrogen cycle will not begin until you add the fish, so running an empty tank for several days will not help. Since your fish tank is brand new, you might want to consider making partial water changes of about 25 per cent of the total water volume every few days for the first week or so.