yes, Hello logley and Welcome to TFF!
Excellent intro there by Wills, agree with all of it. You have luckily stumbled across a real hobby site and I think you'll find a lot of great and friendly people here.
The minimum water volume for the very fancy goldfish is 20G/76L for the first goldfish and 10G/38L more for each added one. For common goldfish its 30G/114L for the first one and 10G/38L for each succeeding one. They need huge spaces, which makes it all the more strange and sad that society has so greatly confused the message about them. They are really a pond fish mostly.
The most important core learning experience you should try to take away from this beginners section is about the "cycling" of your tank and tanks you may own in the future. As mentioned this is a process done to the filter to prepare it for handling freshwater fish. Your first homework assignment within the Beginners Resouce Center should be first the Nitrogen Cycle article then the Fishless Cycling and Fish-In Cycling articles. There also should be a great tank startup article somewhere by Miss Wiggle.
When fish move water through their gills to get oxygen, they give off not only CO2 as waste (like our lungs do) but also ammonia (unlike us, they don't need to preserve water, so they don't have a fancy kidney, bladder and urine system.) This ammonia coming off the gills is actually quite toxic, ironically, to the gills themselves, but is never an issue in nature because there are thousands of gallons of water to dilute it. In the aquarium, without proper filtration, the ammonia, even in tiny amounts causes permanent gill damage, leading to shortened longevity or death in the fish. Fish waste, excess fish food and plant debris are all broken down in the aquarium by heterotrophic/saprotrophic bacteria (not the beneficial ones we want in our filter) and actually -add- to the toxic ammonia load in the aquarium.
For many, many decades the aquarium hobby has had a wonderful tool to handle this problem. Its called the "Biofilter" and is a very odd thing indeed. It consists of a bunch of stuff, like sponges or ceramic gravel, inside a filter, where we grow two specific species of beneficial bacteria to handle the toxic waste of the tank.
The first of these two species, the Ammonia Oxidizing Bacteria (aka A-Bacs for short and actually a set of genetic morphs called Nitrosomonas spp.) take ammonia and process it into nitrite(NO2) as the first step of our Nitrogen Cycle description. Unfortunately, Nitrite(NO2) is also a deadly poison to our freshwater fish. Nitrite(NO2), even in tiny amounts, attaches to the hemoglobin protein on the red blood cells of fish, blocking the oxygen positions and causing a biochemical reaction that changes the hemoglobin into methemoglobin, rendering it unusuable for oxygen carrying from then on. The effect is similar to a human in a closed garage with carbon monoxide: brain and nerve damage are permanent and happen very quickly.
The good news is that our second species of beneficial bacteria, the Nitrite Oxidizing Bacteria (aka N-Bacs and actually Nitrospira spp.) will readily take this Nitrite(NO2) and process it in to Nitrate(NO3) which is not nearly so toxic to fish. We can then remove the NO3, along with lots of other different sorts of negative things via a weekly gravel-clean-water-change that is a basic part of our maintenance habit.
So that's the magic of the "Biofilter" and we work hard to get it up and working well for our fish. In a very small tank like yours, its somewhat more doable to perform a Fish-In Cycle, as has been described. The size of the water changes are not so bad, although they may still drive you crazy near the end of the month or so they might take. A fishless cycle can be frustrating too, as you are testing and watching for a long time while these very slow-growing bacteria develop to sufficient colony sizes.
One thing you will need no matter what is a good liquid-reagent based test kit. Salifert makes the very best of these but they come as individual kits and are perhaps a bit more involved with tablets or powders. Most of us use the API Freshwater Master Test Kit and like it, myself included. The Nutrafin Mini-Master Test Kit is another that works out pretty well. There are still others we don't prefer as much. The tests needed are those for Ammonia, Nitrite(NO2), pH and Nitrate(NO3). Its good to have a couple of syringes from the drugstore to use with the kits.
By now you're probably thinking we're nuts
but its just one of the wonderful things of hobby forums that you can be "jumpstarted" past all sorts of problems that in the past might have taken a long time to learn. Good luck!
~~waterdrop~~
