How Many Fish Go in a 30 Gallon Marine Aquarium?

Saltwater marine aquariums are the most beautiful of all hobby aquariums. Setting up a saltwater tank seems difficult, but it is not much harder than setting up a freshwater aquarium. Extra care must be taken during the set up and initial stocking phase, but if you follow a few general rules, your tank will be running in no time.

  1. The Inch Rule

    • The most surefire way to know how many fish can fit in an aquarium is the "Inch Rule." Basically you are able to safely accommodate 1 inch of fish per gallon. For example you can fit 30 inches of fish (measured from nose to tail) in a 30 gallon aquarium. An example of a fully stocked 30 gallon aquarium might include two 3-inch clownfish (6 inches of fish), three 2-inch damsels (6 inches of fish), and two 3-inch wrasses (6 inches of fish). That only comes to 18 inches of fish total, but under-stocking in the beginning will ensure the tank stays clean and the fish will not be under unnecessary stress.

    Creating a Community

    • When stocking a saltwater aquarium, choose fish that do well in a community and avoid overly aggressive species of fish. If you chose to create a reef tank, you can add corals and invertebrates like crabs, shrimp and starfish that not only make the tank more interesting, but they also help process waste and clean the tank. One thing you must remember when stocking a saltwater aquarium is to start with inexpensive starter fish like damsels, then introduce new specimens once the tank is established.

    Identifying Stress

    • The goal in stocking a saltwater aquarium is to create a community of fish, corals and invertebrates, all living happily together. However if fish are mishandled in transport, put in an overstocked tank, or are mismatched with incompatible species, they can endure high levels of stress which lessen their chances of survival. Signs of stress common in most fish include: erratic behavior, gasping for breath, excessive hiding and aggression.

    Test the Water

    • While the "inch rule" gives you an idea of how many fish fit into a 30 gallon aquarium, testing the water regularly for pH, ammonia levels and nitrate/nitrite levels gives you certainty about aquarium health. Testing the water regularly gives you instant feedback on whether your tank is overstocked or you are overfeeding, both of which are notorious for throwing aquarium chemistry out of balance.

    Have Fun

    • Saltwater aquariums are a challenge to master, but a basic saltwater tank is easy to set up and will reward you with hours of enjoyment. Just remember to allow the tank ample time to become established, and add only a few fish at a time. Get to know each fish and its place in the community. Over time you will have created the reef of your dreams, and your fish will thank you for your patience.