The wisest advice for any tank owner is that maintaining a stunning reef tank, full of healthy corals, is just the net result of maintaining high-quality and stable water. Almost every success or challenge with reef aquariums is closely related to maintaining your water chemistry.


Healthy corals in reef tank


With that in mind, your tank’s water will never be better than the freshwater you start with and this is exactly why RO/DI systems are so popular.


Reverse Osmosis deionization or RO/DI systems are freshwater filtration systems that use a series of sediment, carbon, membranes and resins to remove impurities and filter tap water to be lab quality with zero total dissolved solids (TDS).


This is 99.9% pure H2O and should really be the only water that ever gets used in your saltwater aquarium, both for freshwater top off and when mixing saltwater at home. The best part is, RO/DI systems require minimal effort and can easily be installed in under 15 minutes with roughly 20-30 minutes of maintenance annually.


BRS RO/DI System


Why do I need an RO/DI system?

Almost every single successful reefer uses an RO/DI system because your home’s tap water or well water contains all kinds of impurities ranging from disinfectants to heavy metals. Chlorine, ammonia, nitrate, phosphate, silica and even heavy metals like copper and iron can all be present in your tap water.


These contaminants are usually at levels that pose no threat to humans but can be deadly to the fish, corals and invertebrates inside your tank that breath the water they live in. Not to mention many of these contaminants can heavily contribute to nuisance algae growth in your tank.


Bulk Reef Supply Reverse Osmosis Systems


You can purchase RO/DI water from any local fish store that focuses on saltwater animals but having a system at home is far easier and saves you money in the long run.


Setup and Installation

The best RO/DI system for beginners is our simple Bulk Reef Supply 4 Stage Value RO/DI System - 75 GPD. This will produce zero TDS water appropriate for reef tanks and is completely upgradeable should you decide to add optional stages or accessories.


Bulk Reef Supply RO/DI Videos


With a portable system like this, you can mount it on the wall, under the sink or choose to store it away for use only when needed. The most common installation is a permanent attachment to the wall of your garage, basement, laundry room or wherever you will be making saltwater. They have steel brackets that easily mount to a flat surface using a couple of toggle bolts or even drywall anchors.


Our systems include a faucet and garden hose adapter for feedwater connections or you might want to pick-up an inline adapter for permanent connection under your sink. There are three separate ¼” water lines; the red line is your tap water feed, the black is wastewater to go down the drain and the blue is your product water. One important note, always feed the unit from your cold water line because hot water will ruin the membrane filter.


RO/DI System feed water and drain water connections


The exact installation is up to you but the permanent mount with fixed feed water and drain line connections are really nice. It just makes it easier to use meaning easier to mix water meaning less likely to procrastinate tank maintenance.


What To Expect

Before use, you do want to flush the filters for a few minutes so as not to clog downstream filters with dust or residue from a new filter. The GPD or gallons per day indicates how much water can be produced in 24 hours, give or take a few gallons. 75 gallons per day comes to about 3 gallons per hour so it is not fast by any means. You will also have wastewater at the ratio of about 1:3 product to waste.


RO/DI Filters and Media


For maintenance, most people change out the sediment filter when it looks dirty, carbon filter(s) once per year and the DI resin when it changes color from blue to gold. Once the gold is about ½” from the top, you need to change it out.


The heart of your RO/DI system is the RO Membrane which sits horizontally on top and will last anywhere from 12-24 months give or take. The rate at which all of the filters exhaust varies based on the quality of the input water and usage.


What’s Next

The next logical question is “How do I turn this pure freshwater into saltwater?”. This is even easier than setting up an RO/DI system but Ryan shares some valuable tips to help you avoid some costly mistakes.


5 Minute Saltwater Aquarium Guide Episode 10 - Making Saltwater


You can binge the entire 5 Minute Saltwater Aquarium Guide playlist right here on our website. We also invite you to join the #askBRStv Facebook Group which is a free resource for you to ask questions, get advice or simply get your daily reef aquarium fix.