Stackable Neck Extension for Reef Octopus Skimmers These stackable extensions are designed to extend the neck of Reef Octopus skimmer to achieve greater improvements in filtration and refined control. By adding onto the length of your skimmers neck you increase dwell time achieving greater contact time with dissolved organics and allow for higher internal water height settings. This is an easy way to upgrade the performance of an existing Reef Octopus skimmer without having to purchase a new skimmer. NOTE: The "Twist & Lock" extensions for the Elite and Prime skimmers are white pvc and& the traditional o-ring extensions are only available in black acrylic.