Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
Basically everything you could ask for in aquascaping. I usually get another algae scrapper for the algae that grows on the inner glass of the tank but some people use the sand shovel as well. Great value for what you paid. Except the waiting is 30 days since it's imported from the US.