Our cores are engineered and molded (not drilled PVC) which allows for the even flow of water through the entire cartridge providing these Advantages: Spa Vacuums - Simply remove Dust, sand and particles from a pool or spa Using these hand held vacuums. H2o Capacity: 156 gallons They sent me https://www.reviews.co.uk/company-reviews%2Fstore%2Fjt-spas