Building and maintaining a successful aquarium depends largely on knowing and following best-of-practice procedures based on the collected experience of experts and enthusiasts. After outfitting your tank with the necessary equipment to establish the optimal environment for your aquaria, the next step toward success is selecting the species that are compatible with one another. Our Compatibility Charts will help you select new fish that are most likely to successfully co-exist with established tankmates. Understand that the chart is a guide only and that fish, like people, are individuals with distinctive "personalities." A particular fish may react differently than what is indicated in the chart when exposed to an unfamiliar environment. In terms of compatibility, remember that the larger the aquarium, the easier it will be to mix fish with different behaviors. Many species are very territorial, and even more passive fish can exhibit territorial behavior if you try to maintain too many fish in an inappropriately sized tank. Also, a fish's behavior will change the longer it is kept in captivity. It is advisable to add smaller, more passive fish first, gradually working up to larger, more territorial fish. Introducing new fish Correctly introducing new fish to your aquarium is important not only for the health of the new fish, but for your existing fish as well. When incompatible fish are added to an aquarium, the weakest fish will be stressed, which could result in disease that affects all of the inhabitants of the tank. For this reason, we highly recommend that all marine aquariums be equipped with a properly sized UV Sterilizer to reduce the possibility of disease. After following the step-by-step Acclimation Procedure for your new fish, here are a few tips we recommend to make the transition to its new home as stress-free as possible for your new tankmate: Provide plenty of hiding places for your new arrival. Rocks, plants, and other sheltering areas will reduce aggression and thus stress in the aquarium. Maintain good water conditions through proper maintenance to ensure a healthy environment during this stressful period. Try to add more than one fish at a time to an established aquarium. The chance of one particular individual being singled out and harassed will be minimized. Always feed your aquarium before any new fish are introduced. This will help to reduce aggression toward new tankmates. Rearrange decorations in the aquarium before the introduction to distract existing fish and remove established territories. This will help the new fish by putting it on equal ground as new territories are developed by all tankmates. By following these tips and adhering to the other pre-introduction principles of proper selection and acclimation, your new and existing tankmates will have the best possible opportunity for a smooth transition with minimal stress.