A freshwater community fish tank is the most popular style of aquarium setup: an aquarium with a moderate pH, alkalinity (KH), and GH, populated by several types of hardy, low-aggression fish. However, with all the types of freshwater fish available in the hobby, choosing fish for this type of aquarium can be difficult, especially when attempting to match adult size, aggression levels, schooling requirements, and many other factors that play a role in the compatibility of fish. The first step to considering new stock is to ask some preliminary questions
Question 1: Is your tank big enough?
In general, you will want to keep approximately 1" of adult fish per gallon of aquarium water. This rule can be stretched when large amounts of high-quality filtration is used to prevent waste spikes and nitrate buildup (we recommend Matrix for this purpose), but some types of fish will become notably stressed by overcrowding even if their waste is being efficiently managed. You will also need to account for the fact that some fish need to be kept in groups in order to be healthy. If you only have enough room for one more fish, it will need to be a non-schooling fish.
Question 2: What are your water parameters?
Many freshwater fish available in the hobby today are adaptable to a wide variety of water parameters (pH, alkalinity (KH), GH, and temperature), but some fish have more specialty requirements. Look up your fish species to know what parameters they prefer, and test your water to make sure that the new fish you are considering will fit into your community.
Question 3: Are these fish a good social match for your tank?
Fish are not typically "friends" with other fish that are not their own species, but it is important to match aggression levels and known social behaviors with fish that are already in your system. A fish that is highly aggressive will not be a good match with a tank that contains mostly timid and non-aggressive fish. Likewise, any fish, no matter how timid and non-aggressive, will be happy to eat any fish it can fit into its mouth. Very large fish are never a good match with very small fish.
Now that you have considered the factors which make a fish compatible or incompatible with your aquarium, we can take a look at some sample tank setups. These are all suited to a neutral pH and moderate KH and GH.
Nano Tank (5-10 gallons)
Most nano tanks are better suited for single-species setups, but there are a few exceptionally small fish that can be kept together in a nano tank. Keep in mind that nano tanks tend to be significantly more difficult to successfully maintain than larger tanks, so it will be important to closely monitor your water parameters and carry out regular water changes.
|3 Otocinclus||5 Dwarf Rasbora||3 Sparkling Gouramis||3 Thorned Nerite Snails|
|5 Cherry Shrimp||5 Celestial Pearl Danios||1 Mystery Snail||5 Emerald Dwarf Rasbora|
Small Tank (10-20 gallons)
This is the size of aquarium that most new fish keepers are familiar with, and is suitable to house some of the more common small fish in the hobby. Any of the fish from above can be housed in a tank of this size, but will need to match in size with the other tank occupants.
|5 Otocinclus||5 Neon Tetras||2 Honey Gouramis||3 Nerite Snails|
|5 Amano Shrimp||5 Raspbora Het||5 Zebra Danios||5 Neon Rasboras|
|3 Peppered Corydoras||3 Kuhli Loaches||5 Marbled Hatchetfish||1 Bristlenose Pleco|
Medium Tank (20-40 gallons)
At this size, the fish keeper has a lot of flexibility in terms of setup. Any of the fish from above can be housed in a tank of this size, but will need to match in size with the other tank occupants.
|5 Black Skirt Tetras||5 Congo Tetras||2 Dwarf Gouramis||5 Mystery Snails|
|5 Serpae Tetras||3 Yoyo Loaches||3 Panda Corys||1 Upside Down Catfish|
|1 Angelfish (caution - can be aggressive)||5 Emperor Tetras||5 Gold Barbs||1 Bristlenose Pleco|