Replacement Ballast Transformer for Evolution Aqua Evo UV Clarifier Ballast:15 W 2021 or Newer Unit Height extendable for larger filters Filter Pond Size_ 2400 Gallons Height extendable for larger filters and pumps The open character of this filter media allows for high volumes of water to pass through without cogging while providing optimal surface area to facilitate bacterial colonization the correct models are: Ballast Box Spare 15w EA Pond UV SPBAL2115EAP Ballast Box Spare 25w EA Pond UV SPBAL21250EAP Ballast Box Spare 30w EA Pond UV SPBAL2130EAP Ballast Box Spare 55w EA Pond UV SPBAL2155EAP Ballast Box Spare 110w EA Pond UV SPBAL21110EAP