That will depend on what you intend to host in your tank. Each species has an optimal temperature range. This goes for fishes, plants, snails, shrimp and whaterver you might want to put in there. read more
Ideal range for healthy freshwater aquarium: Below 40 ppm Ideal range for healthy saltwater aquarium: Below 40 ppm, 0 is ideal Reason to test: Waste product resulting from biological filtration that builds up over time. High levels can stress fish and cause algae blooms. Solution: Perform a 25% partial water change and add Tetra® EasyBalance® Solution. read more
Cold water fish do better in temperatures well below that, some of them enjoy water well below 70°F, which is not suitable for any tropical fish. Ultimately the best temperature will depend on the species of fish in the aquarium. read more