I think they work. These sponges have made my water very clean. It's ironic because I only bought the power filter kit to replace the filter with a cheaper and much smaller sponge that seems to work MUCH better. The only thing I don't like about this product is that it doesn't fit an air stone! So I set it as low as possible and limited the airflow with valves so the bubbles were smaller and less noisy. Looking at it from one spot after installing it, I wasn't sure if that reaction was fear or awe.) Pretty good overall!
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