Why do I need two pumps for a Cetus Sieve?

If the Cetus Sieve is installed on a system with a biological filter such as a Nexus, you will need two pumps to install the Cetus Sieve as recommended, this ensure the optimal performance of both the Cetus and biological filter. If the Cetus is gravity fed you could use one pump but this would mean the biological filter would be raised above the pond. Only one pump is required if using with a pressurised biological filter such as a K1 MicroBead, the Cetus MUST be gravity fed.