To calculate the overall star rating and percentage breakdown by star, we do not use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
Does exactly what it advertises. Polishs water to crystal clear. But it get clogged QUICKLY. Even in a relatively clear tank. My suggestion would be only use this periodically, like when rearranging hardscape or replanting to polish your water of all the crap you kick up, then toss it after a few hours once it's done it job. Good luck cleaning it and reusing it like other sponges.