Pro Clear UV30: Suitable for ponds of up to 3000 gallons (13650 litres) with a maximum flow rate of 3000 gallons (13,500 litres) per hour. Pro Clear UV55: Is suitable for ponds of up to 5,500 imp. gallons (25000 litres) with a maximum flow rate of 4,000 imp. gallons (18,000 litres) per hour.