An Article from FK Member Peediepixie giving advice on keeping Goldfish.

So, you've decided you want to keep some goldfish, what is your next step?

The Tank
First you'll need to find a home for them. The goldfish you buy in shops are just babies and therefore still have a lot of growing to do. Common goldfish (slim bodies and single tails) can reach up to 10 inches in an aquarium and fancy goldfish (rounded bodies and double tails) can reach up to 8" in an aquarium so you need a big tank for them. An ideal goldfish tank is at least 3 feet long to give your fish plenty of space to swim and grow properly. Contrary to popular belief, fish do not grow to the size of their tank. There are many factors which can affect a fish's growth and development, the size of the tank is not one of them. Fish can suffer a variety of health problems if housed in a tank which is too small for their needs. This website recommends the following minimum tank sizes for keeping goldfish:

Common Goldfish:
40 gallons (48 US gallons, 180 litres) for the first fish with an extra 12 gallons (14 US gallons, 55 litres) for each extra fish. The tank needs to have a minimum length of 4 feet (120cm) to allow swimming room. Single tail goldfish are more suited to a pond when they are near full size to give them swimming room.

Fancy Goldfish:
30 gallons (36 US gallons, 140 litres) for the first fish with an extra 10 gallons (12 US gallons, 45 litres) for each extra fish. The tank needs to have a minimum length of 3 feet to allow swimming room.

In addition, an external filter is highly recommended.
Your tank may look empty with your baby fish in it but they will grow quickly and fill it nicely.

Remember to do a fishless cycle on your new tank before adding the fish! Your tank may look empty with your baby fish in it but they will grow quickly and fill it nicely.


Decor
Goldfish like to root around in the substrate for their food so make sure that your substrate is of a safe size, either small enough that they won't swallow it or large enough that they won't get it in their mouth in the first place.
Be careful of which plants you put in the tank and goldfish like to eat plants! Java fern and anubias are fairly goldfish proof and look lovely.
Goldfish can get quite rough if they are performing mating behaviour so be wary of adding any sharp objects which may hurt them. Round rocks and smoothed off bogwood look great and provide anchors for java fern and anubias plants. You could create small caves and bridges as goldfish like to explore.


Water
Common goldfish are true coldwater fish but the more delicate fancy goldfish do better in slightly warmer water, around 22C is ideal. They are very easy fish to keep in that they are very adaptable to varied water types but they prefer a ph of 6.5-8.5. Generally, as long as ammonia and nitrite are 0ppm and nitrate is less than 40ppm they will do well.


Maintenance
As with most fish tanks, your goldfish tank will need a partial water change of around 20-30% on a weekly basis. An easy way to do this is to use a gravel siphon which sucks all the debris out of the substrate whilst removing dirty water at the same time. You should then replace the water removed with fresh, dechlorinated water which has been brought to the temperature of the tank using boiled water if necessary. You may also need to clean your glass, rocks etc at the same time. Anything out of the tank should be cleaned using your old tank water so as not to kill off any good bacteria which may have colonised there.
Similarly, every goldfish tank needs a substantial filter to cope with the large amount of waste they produce. This should be cleaned monthly. Squeeze any dirty pads in old tank water, you may want to rinse any biological media (like plastic stars etc) in old water. You will probably need to replace your filter wool/pad (usually white in colour) once a month too. If you have more than one of these white pads, just replace one of them. If you only have one, just cut it in half and replace half at a time.
All this should keep your tank clean and healthy for your fish.


Feeding
Goldfish love food! Dried food such as flake and pellets are fine. However, you should take care when feeding dried food to fish, in particular the rounded fancy goldfish as it an swell in their stomachs as it absorbs water and cause pressure on the swim bladder. To combat this, soak any dried food before you feed it to your fish.
They also love dried bloodworm etc but again, soak before use. Foods such as bloodworm etc should be fed only once a week or so as it is high in protein and fat.
For a healthy fish supplement their diet with fresh fruit and vegetables. As a general rule fish can eat pretty much fruit or veg, just peel anything with a tough skin, blanche anything hard and chop up anything too big. Veg such as cucumber or courgette is a favourite, weigh it down, let the fish enjoy it for a day or so them remove any leftovers. Garlic is good for your fishes immune system and can be fed on occasion also.


Tank Mates
It is generally best to keep goldfish with other goldfish. Fancies do best when kept among their own kind as the faster more streamlined common goldfish will be first to the food and may bully the slower and sometimes more poorly sighted fancy fish.
You can keep other coldwater fish such as White Cloud Mountain Minnows (WCMMs) with goldfish but the danger is that when the goldfish get big enough, the smaller fish may become lunch! Goldfish will potentially eat anything they can fit in their mouth.


And finally...
You've got your nice big tank set up and arranged to perfection, your tank has been cycled and is safe to add your fish. Remember to introduce them slowly, float the bag they fish come in the tank water for 20 minutes or so to equalise the temperatures. Then gradually add some tank water into the bag, a cupful at a time, until you've got more tank water than 'bag' water (I add a cupful every 15 minutes or so). Then place the fish in your aquarium and throw away the water in the bag.
Keep an eye on your water tests over the next week as the addition of fish can mean that you may need to do additional water changes. Add your fish only a few at a time so as not to overload the filter. Enjoy!