Understanding Water: RO, RODI, Distilled, and Tap Water

If you’ve been in the hobby for a week, a year, or a decade, you know that water quality is crucial for the health of your freshwater aquarium. But what type of water should you use? Tap? RODI? How do we know which water is best for our fish? In this article, we’ll explore the differences between RO, RODI, distilled, and tap water, and help you choose the right one for your aquarium life.

Table of Contents

• What Is RO Water, and How Is It Used in Aquariums?
• How Does RODI Water Differ, and When Should You Use It?
• Is Distilled Water a Good Choice for My Aquarium?
• Can I Use Tap Water in My Freshwater Aquarium?
• How Do I Choose the Right Water for My Aquarium?
• How Do I Prepare Water for My Aquarium?

What Is RO Water, and How Is It Used in Aquariums?

RO (Reverse Osmosis) water is specially filtered that removes impurities like chlorine, minerals, and heavy metals. It’s a popular choice for aquariums because it gives us greater control over and consistent to water quality.

Pros: RO water is very pure, making it a good choice for delicate fish and plants. You can adjust the water’s hardness and pH to meet specific needs by adding a remineralizing tank. Just be sure it’s adding back minerals that are safe for the fish.

Cons: For most fish, RO water is not ready to use right out of the filter. You’ll need to remineralize it, which takes time and knowledge. Here is what I use to remineralize my tanks: For Higher PH tanks, 7.0+, I use Salty Shrimp Minerals (it says shrimp, but it’s great for all fish who need minerals with a higher pH). For lower pH requirements, I use Salty Shrimp gH+.

RO water is a great choice for soft-water, low pH, fish like Discus and certain types of plants that thrive in low-mineral environments.

How Does RODI Water Differ, and When Should You Use It?

RODI water goes one step further than RO. After the reverse osmosis filtration process, it’s passed through a deionization filter. This removes nearly all remaining ions (science), leaving ultra-pure water. This water has nearly nothing inside it.

Pros: Like RO water, RODI is incredibly pure. The purest. It’s the best choice if you’re keeping very sensitive species that need very specific water parameters.

Cons: RODI also needs remineralization before use. It can also be more expensive due to the additional filtration step.

RODI water is usually used in reef aquariums, but it can be useful for freshwater setups with sensitive species too. I use it on my Caridina shrimp and my German Blue Rams.

Is Distilled Water a Good Choice for My Aquarium?

Distilled water is boiled and then condensed, leaving most of the impurities behind. It can be similar to RODI in terms of purity, but it’s easier to find in stores.

Pros: Distilled water is almost as pure as RODI water. It’s convenient if you only need small amounts, or if you’re not looking to invest in an RO or RODI system.

Cons: Like RO and RODI water, distilled water lacks minerals. So it will need to be remineralized. It’s also not cost-effective for large tanks because you have to buy it in bottles or boil lots and lots of water.

Distilled water is a good option for small, delicate freshwater tanks, or just for topping off water in tanks where you closely monitor the mineral content.

Can I Use Tap Water in My Freshwater Aquarium?

Tap water is readily available and often contains minerals that can benefit your fish. That’s nice, no remineralizing! However, it may also contain chlorine, chloramine, or heavy metals, which can be harmful. That’s not better.

Pros: Tap water is convenient and cheap. It’s usually suitable for most fish if treated properly and conditioned. The minerals in tap water are usually good for most fish species.

Cons: Tap water quality varies by location. It may contain very high levels of chemicals like chlorine or ammonia, which must be removed with a water conditioner before use. And if the levels are high enough, you made need to use extra. Be sure to test your tap water to get a baseline for what’s in it, and keep in mind that contents of water changes if you live in areas with heavy weather fluctuations or farming in the area.

How Do I Choose the Right Water for My Aquarium?

Choosing the right water depends on the needs of your fish and/or plants. Soft-water species like Discus or German Blue Rams will do better with RO or RODI water. This is because of it’s purity and acidity, lower pH. Hardier fish like Guppies or Mollies often do best in treated tap water.

If you’re unsure, start by testing your tap water. If it’s unsuitable, consider using RO, RODI, or distilled water and adjust it to meet your aquarium’s needs.

h2 id=”preparing-water”>How Do I Prepare Water for My Aquarium?

RO/RODI/Distilled Water: You will likely need to remineralize this water before adding it to your tank. Use a product designed for aquariums to add the right balance of minerals back into the water. For higher pH or less acidic water, us SaltyShrimp kHgH+. For more acidic, or lower pH water use SaltyShrimp gH+.

Tap Water: Always treat tap water with a conditioner to remove harmful chemicals. Here’s a popular water conditioner on Amazon.

After preparing the water, test it again to make sure it meets the needs of your fish. Adjust as needed.

If you have any questions or comments, feel free to share them below! I’d love to hear from you and help you make the best choices for your aquarium.