What is a community tank?

A community tank is an aquarium set up to house multiple species together that can share the same space without fighting, eating each other, or stressing each other out. Think of it like picking roommates: they need similar water preferences (temperature, hardness, pH), similar temperaments, and they have to fit in the same "lifestyle" in terms of swimming level and diet. Most community tanks are freshwater because there are a lot of peaceful, compatible options, but you can do a saltwater community too if you plan carefully. In a good community tank, you mix fish that occupy different zones so they are not all competing for the same territory. For example, you might have midwater schooling fish (tetras, rasboras), bottom dwellers (corydoras catfish), and a calm centerpiece fish (a dwarf gourami or a pair of peaceful cichlids depending on the tank size). Schooling fish usually need a group of 6-10 or more of their own kind to feel secure, and that alone shapes how big the tank needs to be. A lot of "beginner community" setups start around 20 gallons, and 29-40 gallons gives you way more flexibility and stability. Compatibility is about more than "won't kill each other." Watch for fin nippers (some barbs can be rough), fish that outgrow the tank (common plecos), and species with very different temperature needs (goldfish are cooler-water fish and generally not community tropical tankmates). Also pay attention to adult size, not the size at the store. A 1-inch fish that grows to 4 inches changes everything. Practically, a community tank runs best when you stock gradually, quarantine new fish for 2-4 weeks if you can, and keep up on maintenance. A solid routine is a 25-50% water change weekly, test ammonia and nitrite especially in newer tanks (both should read 0), and keep nitrate ideally under 20-40 ppm depending on your setup. Feed small amounts 1-2 times per day so everyone eats without leaving a bunch of food to rot, and provide plants, wood, and caves so shy fish can get out of the line of sight of bolder ones. The goal is a tank where every species can act naturally, not just survive.