Pick a tank. A good rule of thumb on tank size: “Plan for an inch of fish for every gallon of water.” Ready a location near an outlet and away from direct sunlight and vents.
Prep the habitat. Clean the tank with baking powder paste and use a water-vinegar solution to wash the gravel. Set the gravel and any decor in the tank and add tap water and dechlorinator, then let the setup sit a week to let the chemicals in the water evaporate. Test the pH, nitrite, and ammonia levels before connecting a filter and heater, and run both at least 48 hours.
Add fish. Add one fish at first, and up to a few more in a week. Release each fish only after the water in its bag has gradually been brought to the tank-water temperature. Plan on replacing 10 to 30 percent of the tank water each week with water that’s been aged a week itself.
Source: Martha Stewart Living