Choose the Right Tank Setup: To start a three-guppy tank, use at least a 10-gallon aquarium with a gentle filter, adjustable heater, thermometer, gravel or sand substrate, and live or artificial plants for shelter. Cycle the tank before adding fish so beneficial bacteria can establish and keep ammonia and nitrite levels safe. Add a water solution to remove chlorine. maintain a temperature of around 74–80°F, and test the water regularly to create a healthy, stable environment for your guppies.