The Laguna PT8171 is the correct replacement pond filter for the following:
The Laguna PT8171 - Foam Pond Filter for PT8170 is a replacement foam filter for the Laguna PT8170 Starter Kit. This pond foam water filter helps capture debris and other waste in your pond water. This pond foam filter is constructed with highly efficient material that is easy to replace.
Laguna PT8171 - Foam Pond Filter for PT8170 specifications: