Using water straight out of your tap to fill or top off your aquarium is a big no-no. Tap water contains a variety of chemicals that can harm sensitive aquatic life or fuel nuisance algae growth. Running tap water through a reverse osmosis (RO) or reverse osmosis/deionization (RO/DI) system before adding it to your tank removes most of these impurities before they ever enter your aquarium, halting many of the common issues hobbyists face before they ever start.
For a freshwater aquarium, a standard RO system will suffice. For a reef aquarium, you’ll want to use the purest water possible so a RO/DI system will be your best bet. In addition to filtering out pollutants like chlorine, chloramines, nitrates, nitrites and phosphates, deionization removes nearly all mineral ions including calcium, iron and copper.
Most reverse osmosis systems look and operate the same way. Incoming tap water is filtered by the system and exits through two ports: product water (purified for tank use) and waste water (suitable for watering plants, washing clothes, etc.) In a RO/DI system, the product water is filtered once more through a DI filter cartridge for final purification.
An important factor to consider when choosing a reverse osmosis filter is how many gallons per day (GPD) the system can produce. Although tap water quality, pressure and temperature—as well as the age of the cartridges and TFC membrane—affect performance, generally speaking, the GPD rating will be a good indicator of how much purified water a system can produce in a 24-hour period. Depending on your budget and tank size, you might opt for a unit that produces 50 GPD all the way up to 300 GPD.
Reverse osmosis systems must be monitored with a TDS meter so you know when it is time to replace the sediment, carbon and DI cartridges as well as the TFC membrane. Staying vigilant will ensure that the water you are putting into your aquarium is always of the highest quality possible.
We understand you may have questions so we encourage you to contact our aquarium experts for free and friendly advice. You can also learn more by reading Setting up a RO or RO/DI Tap Water Filter, How to Replace Your RO/DI Filter Cartridges, Remove Chloramines with your RO/DI Filter System and Booster Pumps: What They Do and Why You Need One.