A common mistake in the aquarium hobby is to run the output from an R/O filter directly to a mechanical float switch on the aquarium filter to compensate for evaporation. An R/O filter produces its best water quality when run for an extended period of time. Therefore the ideal top-off system begins with a reservoir that is filled periodically by an extended run of the R/O filter. Water is then pumped, via a peristaltic dosing pump such as the Aqua Medic SP3000, from the R/O reservoir into the aquarium filter on-demand as water evaporates. Obviously this type of top-off system requires a reliable level sensing system within the aquarium filter and a switching controller to operate the top-off pump to maintain the water level. The Aqua Medic Niveaumat is an excellent integrated solution that combines the SP 3000 dosing pump with a directly connected low-voltage float switch. Everything you need in one economical package.