When buying new fish for your small aquarium, try to avoid the “I’ll relocate the fish to a larger tank once it outgrows this one” mentality. While a juvenile fish can certainly thrive in a small aquarium regardless of its potential future (provided all of its needs are met), the fish won’t grow any slower because it’s in a small tank. Additionally, it won’t stop growing because it’s in a small tank. Fish grow their entire lives, from birth to death. And over time the fish will get too large for a particular setup, and even though you may have planned a larger setup for it when purchased, things don’t always go according to plan. At that point, your stuck with a pair of tangs in a nano aquarium, with neither one of them remotely getting the swimming space they need. So, if you have a nano aquarium, stick to nano fish.