2 of 2 people found the following review helpful
They are what they're meant to be.,
Verified Purchase(What is this?)
This review is from: Marina Slim Filter Cartridge Compatible x6 Pack S10, 15 , 20 Bio Clear For Clean & Clear Water Carbon or Bio Clear (Bio-Clear Absorbs Toxic Ammonia Reducing Stress) (Misc.)
It's hard to write a review for something when it's the only thing that goes in your filter, but there we go. These work.