PROBLEM: Many people go to the pet store and just start picking out fish for their new tank like an interior decorator picks out new furniture for a mansion. Often the only criteria is what looks good; i.e. the most colorful fish or the most impressive. Occasionally, their checkbook makes the decisions and only the cheap fish are selected. While there is nothing wrong with desiring the nicest-looking fish for your aquarium, or simply being economical, there is often very little thought given to the long term “big picture.” Can your tank really hold that many fish? Will that fish outgrow the aquarium? Stocking the aquarium with either too many fish or fish that are too large can result in several issues, and can end up cost you more money in “repairs.”
ISSUES: Can you imagine sharing a house with 20 other people? What if that house only had one bathroom? Remember that no matter the size, an aquarium is still a closed system and can only handle so many occupants. If the system is overloaded, it cannot effectively provide a healthy environment for all the creatures living inside.
Not all fish are “community” species; i.e. many fish are territorial or even predatory. Mixing any ole’ kind of fish is not recommended without researching that fishes’ habits. Likewise, most fish sold in pet stores are young specimens, and several species can grow quite large, including common goldfish, the “algae-eater” Plecostomas catfish and personable predators such as Oscars. Some of these will routinely grow over 12 inches in length!
SOLUTION: Take care to evaluate your tank size, and research the eventual adult size & behaviors of the fish you wish to keep before stocking the aquarium. In the long run, this will save you money and grief, as well as resulting in a healthy aquarium both you and the fish that live within it will enjoy.