Hello, welcome to Aquarium Advice!
Unfortunately, goldfish are often misconceived to be fish that are extremely durable, especially in small tank sizes. They are quite hardy fish, but eventually they grow quite large, and, like kuhligirl said, need at least a 30 gallon for one, maybe a 50 gallon for two, and on and on. (although, it does matter what kind of goldfish it is, as some grow to 12" and some grow to only 6")
That said, in a 5 gallon you are quite limited, but you can certainly still have a nice tank. In the aquarium hobby, fish known as nano fish are fish that are very, very small, and capable of living in a 5 to 10 gallon tank (generally). Some of those really only do well in a 8 or 10 gallon tank, but there are still many that can live in a 5 gallon.
A betta, of course, is always a good choice for a small tank, however they do
not thrive in 1 pint tanks (yes, I have seen these, it is horrible
). Of course, I wasn't suggesting that anyone might think that, just clarifying. Generally 2.5 gallons is the minimum to give a betta a good amount of room to stay really happy. So a betta in a 5 gallon would be a great little tank, but you could only have one male.
That being said, bettas are not nano fish, so here are some nano fish that you could have a whole school of:
- 5 chili rasboras (boraras brigittae)
- 6 ember tetras
- 6 celestial pearl danios
- 6 dwarf rasboras (boraras maculatas)
- 5 purple pencilfish*
- 3 guppys
- 3 endler's livebearers
- a bumblebee goby*
- a dwarf puffer*
- a pair of scarlet badis (dario dario)*
*these fish are harder to care for than the others, and may not be great beginner fish. A lot of these fish are hard to feed, but are great if you are up for a challenge.
Also, you have to consider shrimp. Red cherry shrimp (RCS) are great small, colorful shrimp, that you could easily have in your tank. You might have 5 of the schooling nano fish (the ones listed with numbers in front) and 5 shrimp. Shrimp have a very low bioload; they don't create much waste, so they don't contribute much to tank stock.
So, those are all good fish, most are good beginner fish too, except for the ones marked by the *.
Now, to get on to something other than stocking. You might need to take this part with a grain of salt. If you don't want to do weekly maintenance, then a fish tank may not be the best thing for you. You
will need to do water changes weekly, but with some knowledge it isn't all that bad. I use the gravel vacuum to just suck the water up (I think most people do this, but if not, then it is much easier than most other things, besides the commercial water changers). You could buy a Python water changer, but for a small tank it may not be worth it.
Also, you need to know about cycling. Here's a brief explanation:
Here, read these links:
http://www.aquariumadvice.com/forums/f12/fish-in-cycling-step-over-into-the-dark-side-176446.html
http://www.aquariumadvice.com/tips-and-tricks-for-your-fastest-fishless-cycle/
The first one is about fish in cycling, the second is about fishless cycling. To cycle a tank you need to get some level of ammonia, and have bacteria in the tank (that get there through the air) to "eat" the ammonia, and make nitrites, which is "eaten" by another type of bacteria that produces nitrates. Ammonia and nitrites are very bad for fish, and levels over .25 ppm of those are bad and can cause permanent damage (given enough time in that water). Nitrates are much less toxic. Nitrates should be under 40 ppm, but under 20 ppm is best. Nitrates are removed through water changes.
A fish's waster produces ammonia, which is the source for fish in cycling. For fish in, you just add fish, test daily, and do a 25 % water change when water gets above .25 ppm for ammonia or nitrites, until you consistently get 0 ammonia, 0 nitrites, and x nitrates. Then, you are cycled (you have built up enough bacteria to "consume" the amount of waste produced by your current stock of fish. This is known as a bioload, the amount of waste a fish produces), and can add more fish, a few at a time.
Fishless cycling uses a source of ammonia (pure ammonia [bottled], a raw shrimp [the kind we eat], or fish food), try to get ammonia up to 4 ppm (but less is okay), and then just add more ammonia when it drops under 4, and do a water change when ammonia or nitrites somehow get over 5 ppm. Once you consistently get 0 ammonia, 0 nitrites, and x nitrates, you are cycled, and can add your whole stock at once. If you don't add your whole stock at once, say add only 5 fish, and then wait a week, you cannot add your whole stock then, as the bacteria will die off until there is just enough ammonia produced for all of the bacteria to eat. While fishless cycling you should test at least every other day.
^^^ That was a post I sent to someone else, and I saved it as a google doc so I could post it multiple times.
Cycling is very important to a tank, and whatever you do, DO NOT add fish before you cycle!
Hope this helps!
