Reverse Osmosis System

Reverse Osmosis System

Reverse Osmosis Systems

In my opinion all saltwater aquarium hobbyist should use reverse osmosis systems for topping off evaporation and mixing artificial seawater, for aquarium water changes. A reverse osmosis system may sound complex, but it’s really a simple form water purification. Water straight from the tap, can often contain excessive amounts of chlorine, copper, nitrates, nitrites, phosphates and many other metals and chemicals. These contaminants are vary harmful and possibly deadly, to sensitive marine fishes, invertebrates and corals.

Tap water can also contain nitrates and phosphates, which can cause excessive algae growth and cyanobacteria outbreaks. The use of both reverse osmosis and deionization is the most popular method amongst saltwater aquarium hobbyist, and is preferred above all other forms of water purification processes. 

How the Reverse Osmosis System Works?

Reverse Osmosis is a process in which inorganic chemicals, disinfection byproducts and other contaminants are removed from water. Household water pressure pushes the tap water through the system’s membrane. The membrane only allows pure water to pass through it’s cell walls, not the impurities and other contaminates. The contaminates are “rejected” and directed to the drain line of the RO system.

  • Temperature.
  • Water pressure.
  • Quality of the pre-filters and membrane.
  • Amount of contaminants in the tap water.

What does a Reverse Osmosis System Remove?

A reverse osmosis membrane will remove contaminants and particles larger than .001 microns from water.

Contaminants often found in tap water:

  • Calcium
  • Chloride
  • Fluoride
  • Iron
  • Nickel
  • Nitrate
  • Magnesium
  • Manganese
  • Phosphate
  • Potassium
  • Sodium
  • Sulfate
  • Zinc

For a full list of tap water contaminants check out the list at, but you will probably wish you diddn’t

Basic components common to all Reverse Osmosis Systems:

  • Water Supply Line: This is the water source for the RO system.
  • Pre-Filter (s):   Water from the water supply line enters the reverse osmosis system’s pre-filter first. There may be more than one pre-filter used in a Reverse Osmosis system. The most commonly used pre-filters are sediment filters as well as active carbon filters.
  • Automatic Shut Off Valve (SOV):  Many RO systems have an automatic shutoff valve. When the storage vessel is full this valve stops (most common a float valve) anymore water from entering the membrane and stopping water production.
  • Reverse Osmosis Membrane:   The membrane is the heart of the reverse osmosis system. The membrane is designed to allow only water to pass through it’s cell like wall, while removing contaminants.
  • Post filter:   After the water leaves the Reverse Osmosis Membrane it will pass through the post filter. The post filter is generally DI resin.
  • Drain line:   The drain line runs from the out the end of the membrane housing or post filter to the drain. This line is used to dispose of the impurities and contaminants removed from the tap water.

Quality of RO Membranes and Filters.

While most RO system look similar the quality of internal components can be very different. These differences can have a significant impact water purification and overall production.

How to Increase your RO systems Water Production.

A higher flow reverse osmosis membrane will improve your rate of production. I started with a 24 gallon a day RO system. With my household water pressure and contaminant level, this gave me about 5 gallons a day. A higher capacity membrane will insures that you have more water available when you need it.

Changing to a higher capacity membrane is easy.  You simply replace your old membrane with a new, higher capacity membrane. Most standard membrane housings will except membranes ranging in production of  25 to 150 gallons per day.

What does RO/DI unit mean?

A RO/DI system is a reverse osmosis system with a post filter filled with DI resin. DI resin removes the smallest of all impurities known as ions,
from water. In short DI resin beads work like magnets, trapping positively charged ions and removing them from then water.

DI resin beads remove the particles that are too small that even for reverse osmosis systems. Even after water has past through the RO system, a few remaining particles may pass through the membrane. Therefore, in order to remove them from the water the use of DI resin, will produce an absolutely pure form of water.

There are many types of DI resin available on the market today. I recommend using the color changing product, so you know when you need to place the DI Rein.

RO/DI system final thoughts.

Success can come in many forms within the saltwater aquarium hobby. To have a amazing saltwater aquarium you must first start with good aquarium husbandry. Tap water is not acceptable for the use of topping off aquarium evaporation and mixing artificial saltwater, let alone for human consumption(in my opinion).

If you don’t use a reverse osmosis system you should and your livestock will thank you for it. For more information on reverse osmosis follow the link. 

Any questions about reverse osmosis systems, feel free to contact me at:

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