While zebra danios and the goldfish both have similar water requirements, pearlscale goldfish reach an adult size of 4+ inches. They are also very stocky fish that produce a lot of waste. I wouldn’t personally keep one of these fish in anything smaller than a 30-gallon aquarium. For five adults, I would recommend no lower than a 55-gallon tank. If you can’t get a bigger aquarium, try exchanging the goldfish for the zebra danios. Zebra danios are small, active fish that will thrive in a 15-gallon tank. You can add at least three or more of these fish and still have room for other coldwater fish species.