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The water you add to your reef tank is the most important factor for any type of success. Municipal, well, and "tap" water sources often contain copper, manganese, lead, nitrate, phosphate, disinfection chemicals and other substances that make will do harm to a reef aquarium full of fish, corals and other invertebrates. The best defense against these contaminants is a reverse osmosis filtration system or RODI. Reef enthusiasts rely on their RO system to ensure the saltwater they mix up is consistently safe for their tanks, containing zero total dissolved solids. The same goes for top-off water. Your reverse osmosis system needs periodic maintenance to keep it working properly. If not, it will allow contaminated water through the system, causing water quality problems in the short and long term. Here’s everything you need to know to maintain your RO or RO/DI system.

Sediment Pre Filter

The sediment pre-filter cartridge is designed to protect the filtration system from clogging or damage caused by fine particles such as iron oxide, sand, and mineral scale. Over time, these small particulates can clog the tiny flow restrictors and activated carbon filters. The pre-filter is made of spun polyester fibers designed to capture these fine particles. As the fibers clog with sediment they also become coated with naturally-occurring bacteria slime. Clogged pre-filters will reduce flow to the rest of the reverse osmosis system eventually. How to tell when to change the RO or RO/DI pre-filters is if the pressure gauge readings decline, otherwise, we recommend these be replaced every six months to maintain maximum water production.

Activated Carbon Cartridge

The activated carbon cartridge follows the prefilter. Your RO may use a granular carbon or a solid carbon block cartridge. The role of the activated carbon cartridge is to remove chlorine and chloramine disinfectants. Activated carbon also removes organic compounds such as pesticides, carcinogenic disinfection by-products and naturally-occurring organics.  Carbon cartridges should be changed about every six months when maintaining your RO or RO/DI system. Just like the prefilter, activated carbon will eventually become coated with slime and stop removing chlorine and chloramine.

Reverse Osmosis Membrane

The heart of the RO system is the reverse osmosis membrane also called the TFC membrane. A semi-permeable membrane is wound around the center core. As water is forced through the membrane, minerals, nitrate, phosphate and metals are stripped from the water and sent to the wastewater line.  The membrane works by “rejecting” the contaminants from the water stream. But they must be flushed away to keep the membrane working.  Over time all RO membranes become fouled with calcium carbonate, bacteria and other contaminants.  How to maintain and extend the life of the membrane is with an RO Flush Kit.  The flush kit loosens and washes away minerals and contaminants that clog the membrane.  The easiest way to monitor the status of the RO membrane is with a TDS meter. Whether hand-held or in-line, the meter will show when minerals and salts begin slipping past the membrane. This signals that the RO membrane needs to be replaced.

Deionization Cartridge

Reverse osmosis alone does not produce extra-pure water. RO removes a percentage of the contaminants. Certain substance like nitrate and silicate are hard for the RO to remove. That’s why a deionization cartridge(DI) is often the last stage in the water purification system. DI uses ion-exchange resins to scavenge out any trace of silicates, phosphate other undesirable substances. Once the resin is used up, it stops working. DI resin cartridges will cause the water to have a “fishy” odor when used too long. If your DI cartridge use color-changing resin to indicate when it needs to be changed, change it as soon as the cartridge changes color. You can also use a hand-held TDS meter to monitor the quality of your water after the DI cartridge.

Filtration is one of the most important factors in establishing long term success as water quality is essential in both freshwater and saltwater aquariums. Almost all displays look beautiful on the first day of setup, but, as that brand new tank look wears off, we begin to rely on our filtration to keep everything looking clean and healthy. Aquarium filters come in many varieties including ones that hang on the back of the aquarium, canister filters that are plumbed externally, and multi-filters that can perform a variety of tasks in the filtration process. Building an aquarium with an excellent mode of filtration allows hobbyists to have the perfect foundation to create a successful saltwater, freshwater, planted, or reef aquarium.

While the look of these products may differ, the ways in which they operate are ultimately the same. Aquarium filters are designed to remove harmful elements from the water, create continuous water flow, and polish the water to keep it clean and clear. Within this list, we will break down some of our best aquarium filter recommendations including the hang on back, the canister filter, and the multi-filter.

Best Hang-on-Back Filter: Seachem Laboratories Tidal Power Filters

This filter is a beast, it is one of the only hang on back filters equipped with a surface skimmer, ensuring excellent function on both saltwater and freshwater aquariums. High quality and well thought out products are what we have come to expect from Seachem and their Tidal Power Filters are a perfect example. These filters come in four sizes and can be used on aquariums up to 110 gallons. One of the best features on this filter is the oversized filtration capacity that allows you to add any of Seachem’s media to the back of the unit. Another impeccable feature in this filter is the custom leveling and flow regulation that allows for a great fit on any tank. Finally, there is a maintenance monitor which will alert you when the media inside needs to either be cleaned or replaced. These features are nearly impossible to come by on any other hang on back filter which is why we have selected the Seachem Tidal Power Filter as one of the best aquarium filters on the market. 

Best Canister Filter: Eheim Classic External Canister Filters

Eheim has been producing canister filters for decades, and it shows in their product. Their excellent build quality, pricepoint, and customer care have allowed them to make this honorable list. These filters come in a variety of sizes to fit your aquarium and each includes a set of media to filter and polish your water. This canister filter features quick disconnect plumbing which allows for easier maintenance and cleaning when necessary. While Eheim filters may lack some of the special features that you can find on more modern and expensive filters, they are a reliable option that is built to last. This makes the Eheim Classic External our choice for the best aquarium filter in the canister category. 

Best All in One Filter: AquaMaxx HF-M Hang-On-Back Multi Filter

As our hobby has progressed, so have our filters, we now have options that perform more than just simple water filtration and polishing. The AquaMaxx HF-M Multi Filter is a shining example of innovation in our industry, it is equipped with a built in protein skimmer, probe holder, tubing holder, and media cartridge. All of these included features come together to make an exceptional all in one filtration unit that can perform on aquariums between 20 and 60 gallons. This filter guides water through three different stages of filtration; beginning with the protein skimmer where waste is removed from the water. The water then enters a biological filtration section where it is polished. Finally, the water flows into the third and final chamber where even more filter media can be customized to suit your system. All of these premium features packed into this single filter provide your tank with a comprehensive saltwater filtration process that cannot be topped without the use of an external sump.