How To Choose Fish That Will Fit Your Tank
One of the most common mistakes new fish keepers make is stuffing fish that are too big into tanks that are too small and then wondering why their fish always seem to be sick, are always fighting or are dead.
1 – 5 Gallons
These tanks are technically nano tanks and are best suited either as individual fighter tanks or as planted nano-tanks with a few small neons in them. Please don't buy a small tank and think you're going to get away with putting goldfish in it. Goldfish do best in ponds, and if they're not available, the best sized tank for a handful of goldfish is 55 gallons. Yes, you read that right. I cannot tell you how much waste goldfish produce and how quickly small tanks will foul if you try to keep them there. I know pet stores sell these little tanks as goldfish bowls, but that's largely because pet stores don't particularly care if your fish die in two weeks time. In fact, they're quite happy if that happens because there's a decent chance you'll be back to buy more.
5 – 10 Gallons
A better sized tank for the beginner, a 10 gallon is perfect for a few guppies or other similarly sized fish. It is not suitable for Angelfish or other cichlids, which grow beyond an inch or two in length. Be aware that if you do choose live bearers like guppies, they may quickly overbreed and fill the tank with babies if males and females are mixed.
The 20 gallon tank is the tank stuck in between worlds. It's too small to really keep cichlids and larger fish, but it seems too large for guppies, mollies and the like. My advice? A 20 gallon can make a lovely planted tank with lots of little fish like the aforementioned guppies, mollies and sword-tails.. If you want a bright tank with plenty of small fish and movement, then a 20 gallon is an excellent size.
Though a 55 gallon might seem like a large tank, if you're planning on keeping fish bigger than guppies, its actually a good size for a first tank. 55 gallon tanks can hold several medium sized chichlids and other compatible fish and their size means that there is the capacity. A 55 gallon is also the smallest sized tank you'd want for keeping solitary big fish, like a single Oscar or a single Jack Dempsey.
Once you start getting into the 70+ gallons range you can start keeping larger fish, like Oscars in greater numbers. A 70 gallon can comfortably house a breeding pair of Oscars, for instance.
These are monster tanks for monster fish like Arowana, or for keeping multiple large fish like Oscars, Jags, Green Terrors and the like. Obviously cost and space restrictions prohibit these from being tanks for the beginner, however they are often the inevitable result for keepers who fall in love with larger fish.