Yescom 40/200/400/800pcs 1.2"/30mm Reusable Bio Balls Aquarium Fish Pond Wet/Dry Canister Filter Media Tank Biofilter 400pc of 1.2" diameter Aquarium Bio-balls Simply Rinse and Use Dense Hole Structure for Nitro-bacteria For use with Wet / Dry filters etc. to improve biological filtration Easy Maintenance