Domestic Oyster Shells 500g (Fine) Oyster shells treated with high-temperature heating. Leaches minerals and calcium. Absorbs chlorine and ammonia, which are harmful to fish, and maintains pH during aquarium setup and water changes. Decomposes components that cause cloudiness and odor in the aquarium water, powerfully purifying it. ●How to Use ・Rinse lightly before use. ・Place this product in a filter media net and set it in an external filter or top filter. (Effective if set in the area with water flow in the top filter ◎) ・Use approximately 300g for a 60cm aquarium. ・After about 3 months, the surface of the oyster shells will become dirty, and the filtration effect will diminish. ・Replace when you feel the effect has decreased. ●We also accept bulk purchases and requests for large quantities. Please write the desired quantity in the comments. (Price will vary due to shipping costs)