The PF501 is a 5th generation fluidised calcium reactor and is suitable for aquariums up to 1100 lts - 245 UK gallons - 290 US gallons normal stocking and illumination.
The 5th generation models now have a new design of aquabee pump to prevent wear due to the abrasive nature of the water and media in the reactor. These pumps are now fitted with a thermal cut out to prevent damage if allowed to run dry.