No discolored water when rinsing the filter cartridge
Before using a filter cartridge, the instructions say to rinse the filter out to remove any discolored water.
If you did not see any discolored water, it does not mean the filter cartridge is defective.
During transportation, a small amount of carbon dust can accumulate inside the shower filter, which gets washed out during the first use.
So if you do not see any discolored water, it means the transportation of the shower filter was smooth, and no carbon dust was produced inside the shower filter.