Aqua One (38s) Replacement for 500/700 Replacement Sponge (Fine Filter Pad)-- Pre-orderAqua One Replacement Sponge Pad designed for:Aqua One Aquis Canister Filters 500 & 700Includes 2 Sponge Pads per pack with a small hole to fit nicely into filter media baskets- Easy to install- Low maintenance..