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Unveiling the Secrets of RODI Water for Aquariums

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Last updated on December 1st, 2023

2023-12-01T20:27:45+00:00

Unveiling the Secrets of RODI Water for Aquariums

When setting up a new aquarium, many are led down the path of filling their tank with tap water and using a dechlorinator to make the water “safe” for fish. The dechlorinator does remove chlorine from the water, but what does it miss? If you can use tap water with a chemical to remove impurities, why use RO Water for Aquariums?

While it's true, tap water generally contains chlorine, it contains much more than just chlorine. Tap water naturally contains phosphates, nitrates, silicates, as well as some metals. Some tap water contains copper, iron, and even small amounts of lead. There are also a variety of other elements and minerals, as well as chemicals used to treat the water, that can be measurable, and dangerous to your aquarium.

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Some of these impurities like copper, chlorine, and other chemicals can kill fish, invertebrates, and even coral. If you are lucky enough not to have these issues, will likely notice a lot of algae growth and slow coral growth when using dechlorinated tap water. This is because the other nutrients and minerals within the tap water feed this algae growth and inhibit coral growth.

What is Reverse Osmosis?

Reverse Osmosis (RO) filters are very simple. Reverse Osmosis is a process where water is forced through at least 3 different types of filter media, known as membranes, to remove impurities. Reverse Osmosis can remove practically everything from the water, including salts, minerals, microplastics, and even chemicals that were added for cleaning such as chlorine.

Reverse Osmosis water is used for reef tanks because it not only pulls out chlorine and cleaning chemicals added, but it also removes metals, undesired elements, and gives you a fresh start before adding salt mix. This filtration can prevent algae, and even unforeseen coral and fish death!

How Does Reverse Osmosis Work

The faucet forces tap water through a series of membranes that catch impurities of different sizes in the different stages of the filter.

Sediment Filter

The first step in Reverse Osmosis is a Sediment Filter. This is like a filter sock for the RO System. Most of the time, sediment filters are 1 to 5 micron filters. This means only things that are 0.001 mm (1 micron) to 0.005 mm (5 micron) can actually fit through the filter. To give you an idea of how small that is, a human hair is 50-90 microns wide. This will remove dirt, dust, rust, and all sorts of other things in the water.

Carbon Filter

The next step in Reverse Osmosis is a Carbon Filter. Like in your tank, the carbon step removes volatile organic compounds (VOCs), chlorine, other chemicals, small elements, and other contaminants in the water. This step will make the water crystal clear and odorless as well! Carbon filters are also commonly found in 1 to 5 microns. Personally, I try to choose the smallest one that is reasonable. I may need to replace it more, but the water it produces will be cleaner.

Usually for reef tanks, you'll want to use 2 stages of carbon. While most drinking water RO units only use a second stage if needed, reef tanks need water to be very pure, to a non-drinkable level. So just assume you'll have a second stage of carbon at a minimum.

RO Semipermeable Membrane

The final step in Reverse Osmosis is a semipermeable membrane. The membrane will remove nearly all of the total dissolved solids (TDS). The other steps before this remove most of the contaminants that would cause the membrane to clog. This membrane is a lot of VERY small layers wound together to a point where molecules larger than water molecules can't fit through! Making the water very pure!

The membrane then has "reject" or waste water. This is the water and the larger molecules that are not able to pass through the filter.

What is Deionization (DI)?

When filtering RO water for aquariums, the filter may not be able to bring the TDS (Total Dissolved Solids) down to zero depending on how many impurities are in your water. Though a 4-stage filter will work for most, if your water has a really high TDS, you may need additional stages of RO/DI filtration. When adding another stage of RO filtration, there are two common options. The first is an additional carbon membrane, mentioned above, the other option is DI or Deionization, Resin. If you need filtration beyond 5 stages however, you will have very limited options without using DI Resin.

Deionization, or DI, uses media containing Cation and Anions. Basically, they neutralize positively and negatively charged ions to remove nearly everything missed by the other stages out of the water. Most of us only need to use mixed Cation and Anion DI Resin, but if you are going to have 2 DI steps anyway, you might as well separate the two so that you can replace them as they are used up.

Cation Resin

The cation resin is positively charged and will neutralize positively charged ions such as calcium, magnesium, aluminum, ferrous and ferric iron.

Anion Resin

The anion resin is negatively charged and will neutralize negatively charged ions such as silicate, sulfates, CO2, nitrate, and phosphate.

Mixed Bed Resin

Mixed Bed resins have both cation and anion resins mixed together. They may contain more of one or the other, but the general concept is that it is a single stage with multiple types of filtration.

RO Booster Pump

Finally, there are ro booster pumps. These pumps are used to increase the water pressure for homes with pressure below 50 PSI. Low water pressure means the water won't be pushed through the filter as well, so your filter will not be as efficient. The tip I read is under 50 PSI with TDS over 500, you need a booster. Most city filtered water won't need this, but most well water homes will need a booster.

Recommended Reverse Osmosis Filters

When it comes to RO Filters, the premise of simple is usually best. As long as the RO filter uses standard membranes, then low cost is key. Here are a few I recommend.

Conclusion

Using RO water for aquariums is a simple way to filter fresh water for your aquarium. Providing an good starting point, free of toxins and impurities for your aquarium. The reduced silicates and phosphates from RO water will also help prevent algae and diatoms from your tank. Essentially, running an RO filter at home provides quick access to high quality water for your aquarium.

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About the Author

Reef Stable Founder John Krenzer

John is a Software Engineer with a passion for saltwater aquariums, as well as the founder and president of Reef Stable. He started in the aquarium hobby as a child with a 20 gallon freshwater aquarium. His interest in aquarium life grew and in 2008, John set up his first saltwater aquarium.

Today, John maintains an over 300 gallon reef tank system, consisting of a 120g reef and a 210g reef. These large tanks are contained within the same system, sharing a sump as a means to reduce total maintenance and increase total water volume.

John writes articles for the blog as a means to learn about more reef aquarium topics. These articles act as a reference for the readers as well as himself. John updates these articles frequently to provide additional information or make corrections as new information becomes available.

If you would like to request an article, tank tour article, or to collaborate, let me know via the Contact Me Page!


Frequently Asked Questions

Is RO water safe for aquarium?

Not only is RO water safe for aquariums, it is an ideal starting point in order to have an impurity free water change. Though this water may be too pure for freshwater aquariums, you can add supplemental minerals to the water to know what your parameters are. For saltwater aquariums, the salt itself is sufficient and no other minerals are needed.

Can algae grow in RO water?

Yes. Algae utilizes light, phosphates, nitrates, silicates, and other impurities to grow. Though RO water itself should not contain these impurities, light alone can allow some forms of algae to grow.

Is RO water necessary for saltwater aquarium?

Yes. RO water is necessary for saltwater aquariums as impurities in tap water can lead to excessive algae growth, slowed coral growth, or even death of aquarium inhabitants depending on the impurities in the tap water.

Can saltwater fish live in tap water?

Though saltwater fish can live in tap water with dechlorinator and salt (obvious), it is not ideal. Tap water can lead to excessive algae growth, slowed coral growth, or even death of aquarium inhabitants depending on the impurities in the tap water.

Can I use distilled water in saltwater aquarium?

Yes. Distilled water works equally as well as RO water for saltwater aquariums as the distillation removed impurities.

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