Philips Standard Double Ended T5/T8 UV Lamps are available in 4w, 6w, 8w, 15w, 16w, 25w, 30w and 55w sizes and are compatible with most brands of UVC. The Standard replacement UV lamps have 2 small pin connections at both ends of the bulb.
To keep your pond clear from algae and green water build up bulbs should be replaced every 8 to 12 months, the recommended time to replace a bulb is at the start of spring just as the pond season starts, this ensures the UVC is at optimum performance for when it is needed.