Reverse Osmosis (RO), Deionized (DI) and Natural Seawater for Reef Aquariums
Reef Aquarium Water Overview:
The water you use in your reef aquarium must be of the highest quality possible. The water from the tap is laden with dissolved organics and heavy metals and chemicals used to clean and purify the water such as chlorine, fluorine and a vast amount of phosphates and nitrates. If you use water from the tap, it must be filtered properly or your reef aquarium will fail.
Like most aquarists, I use a Reverse Osmosis/De-ionizing system (DI) to filter local tap water to a concentration of less than 5 ppm. What this means is that for every million parts of water, namely H2O, there are less than five parts of dissolved metals, organics and other chemicals.
Note: The terms filter and canister will be used interchangeably when referencing an RO/DI system as the system is composed of filtering canisters.
An RO/DI system has many stages in which it reduces the amount of impurities within tap water (starting from the largest and ending with the smallest). The first two canisters on an RO/DI system are sediment filters which use filter floss with progressively smaller mesh. These filters get rid of the large pieces of calcium build-up found in tap water as well as larger pieces of calcium build-up found in the pipes of your local water system. The third canister houses an Activated Carbon Filter which removes organic chemicals and chlorine that could harm where the water flows to next, the RO filter.
The RO filter houses a Thin Film Composite membrane (TFC) and is the limiting factor with how much water can be made in a day. The TFC pores are extremely small (.0001 microns) which will cause the water you’re filtering to flow very slowly; however, there are ions so incredibly small that could pass through the RO filter, endangering the inhabitants of your reef aquarium if not stopped.
Thus, the final step in an RO/DI system is another carbon filter, the DI filter. This canister is filled with an ion exchange resin that removes any remaining chemicals from the water before being added to your aquarium. Both cations from sodium, calcium, iron, copper, and anions such as chloride and bromide are removed with this filter. This is the most important filter for the reef aquarium as it removes any phosphate from the water that, if left, would result in algae growth and de-calcinations of the corals.
When used together, the RO and DI system creates a base-water that is perfect for the reef aquarium. Once you have pure, clear water to start with, you can add your choice of salt to the water to create an ocean-like environment.
When choosing which type of salt mix to use in your reef aquarium, it is very important to understand the difference between “sea salt” and what has been labeled “reef salt”. Instant Ocean is a low-cost, sea salt mixture that has been formulated to be used in fish-only systems; it lacks much of the needed elements for reef systems.
Reef salt, the most common of which is Reef Crystals, is a more expensive and complex salt mixture; elements have been added that make it suitable for reef aquariums. Included in this mix are trace elements like Strontium, Iodine, and Magnesium which are not included in regular sea salt. There are also calcium and PH buffers that are very useful in assuring that the PH will not fluctuate drastically with a large water change.
If you are going to set up a reef aquarium, it is very important to use a high quality reef salt that has been developed for use on reef aquariums. If you decide to use regular sea salt in your reef aquarium, you will have to dose it with all the essential elements that the mix lacks as well as add a PH buffer to stabilize your tanks’ PH. In the long run, it is mush easier to use a high quality reef salt that has all the components your tank needs rather than add components to a cheaper sea salt every time you do a water change.
Using Ocean Water:
Living in South Florida like we do has many benefits, including beautiful weather, great beaches and an exciting night life. There is also the benefit of having access to some of the freshest, cleanest and nutrient laden water around. When high tide comes in, we can go to any local inlet (Hillsboro Inlet is the closest to us) and take water directly from the ocean.
This is only possible because the water coming into the inlet is directly from the Gulf Stream and comes from hundreds of feet deep. If you are going to gather ocean water from the east coast of Florida, don’t use water from the shoreline because of the presence of pollutants and don’t use water from too far inland because it is never fully replaced with fresh Gulf Stream water. If you are not near the east coast of Florida, travel 5-10 miles offshore to gather an ample supply of clean ocean water.
It really is amazing how perfect natural seawater is for reef aquariums. When I get water from the Gulf Stream and test it at home, I get the following parameters:
PH=8.2, KH=11, Ca=420, Ammonia=0, Nitrite=0, Nitrate=0, Phosphate=0
These parameters are pretty much perfect!! Additionally, the water is full of beneficial bacteria, plankton and microalgae that are the perfect food for all the tank inhabitants.
In short, if you have access to fresh, clear, non-polluted ocean water, use it!! It has the perfect natural parameters, contains beneficial microorganisms and is free of cost!! Local reef stores even sell the stuff (often for 50 cents a gallon) and use it in all of their aquariums.
Highlighting the potential environmental benefits of using ocean water, if you place the used seawater from your aquarium back into the ocean, it will be like you never even removed it. If every marine aquarium hobbyist used fresh ocean water, there’s the prospective discontinued need for sea salt factories (which create greenhouse gasses from their manufacturing processes). Additionally, you would not have to use water from municipal sources (which create greenhouse gases from their cleansing and filtering processes).
Reef Aquarium Water Supplements:
Supplements in reef aquariums are almost as prevalent as human supplements (think GNC and all the commercials on TV), so in order to cover all of them, we have created yet another page that will list them by category with a description of what they are, how to use them and how to attain ideal levels for your reef aquarium with them. Just follow the link below to access our REEF AQUARIUM SUPPLEMENT database. We are adding new items daily.