Filters For Marine Tanks
External filtersYou can run a fish-only marine aquarium with an external filter, but it is wise to opt for one with larger or more flexible media trays to allow the use of medias designed for specific purposes. Marine tanks tend to produce less physical waste material, mainly due to a lower stock level, so mechanical (sponge) filtration is required but not overly important. Good biological media, extra room for additional media, and a strong flow rate are the features that you should look for. 'Off-the-shelf' internal filters are too small and inflexible for marine aquariums, although some bespoke or built-in internal filters may be suitable. An external filter in conjunction with a skimmer will provide the minimum but perfectly adequate filtration for a fish only aquarium.
Sump filtersTo run a reef tank properly, you need a greater control over water conditions and the option to add extra items of equipment if they are required at a later stage. For this reason, sump filtration, using a separate tank (the sump) beneath the main tank, has become the most popular option for larger reef aquariums. In a sump system, water from the main tank will overflow through a weir built into the aquarium and into the sump tank beneath where it will travel through various stages of filtration before being returned to the aquarium via a powerful pump. The benefits of sump filtration are numerous but the overriding advantage is that all your equipment is housed away from the main aquarium, making maintenance a lot easier and hiding unsightly pipework, heaterstats, and skimmers from view.
Modifying a sump systemThe essential items in your sump system will be mechanical, biological, and chemical filtration media, a skimmer, heaterstat, and return pump. Alongside these, a sump gives us plenty of room to add other useful items if they are required. Nitrate reactors to lower nitrates, calcium reactors to increase calcium levels for corals, automatic top-up systems to combat evaporation, electronic metering systems and more can all be added easily to a sump system. Whilst some of these units can be incorporated to other systems or run on themselves, using a sump makes everything a lot easier and tidier.