Dymax Algae Wafers Supreme Size:520g Model Number of Cata Pure Hydra Model Number of Cata Pure Hydra Filtron 1000 2 Hydra Filtron 1500 3 Hydra Filtron 1800 4 Hydra 20 1 Hydra 30* 1 (or 1 square*) Hydra 40 2 Hydra 50 2 *For the square cartridge for the Hydra 30 Wireless technology: no probes or messy wires Large LCD display simultaneously shows aquarium and ambient room temperatures This product is produced as a complete daily diet fortified with vitamin supplements and specifically formulated with mostly vegetable materials for sensitive plecostomus The uniquely shaped disc sinks rapidly and retains its shape allowing less aggressive species to nibble over a longer period of time