How much GPH (gallons per hour) do I need?

The common rule cited across r/Aquariums and r/PlantedTank threads is 4–6x tank turnover per hour for community freshwater tanks, and 8–10x for heavily stocked or messy fish like goldfish and cichlids. Manufacturer GPH ratings are typically optimistic — real-world flow drops once media is loaded, so reviewers commonly recommend sizing up one model.