What Is R.O Water And Why Do I Need This?

What is RO “reverse osmosis?”

Reverse Osmosis, commonly referred to as RO, is a process where you demineralize water to create purified water. This is a process that entails water being pushed under great pressure through a semi-permeable reverse osmosis membrane. The membrane will only allow water molecules through and prevent larger molecules such as minerals and other chemicals to pass through.

Reverse osmosis is a water purification process that many marine and freshwater fish keepers use to protect their fish from chemicals and particles in the water which could be harmful. The particles and waste products are left on one side of the membrane and the pure water is left on the other – ready to use.

Why is RO important for the fish tank?

This purified water is ideal to use for marine tanks especially. As tap water can contain levels of nitrates, phosphates and silicates which can cause unwanted algae growths and blooms in the tank and have also been known to kill off sensitive corals – so for marine fish keepers RO and salted RO are the way to go.

It is also important to remember that this water will lack important minerals and chemicals that may be detrimental to the fish’s health and wellbeing as well as important for coral or plant growth. So it is always necessary to dose the water with any vitamins or minerals that are needed for the correct growth and fish in your tank. Also, some freshwater tanks need special care to keep their PH levels stable, fish such as cichlids have more specialised requirements when it comes to water PH, so when using RO water make sure you have a good re-mineralising buffer as this will be beneficial.

Problems with Tap water

Water from the tap will contain high numbers of dissolved solids in the form of salts, phosphates, nitrates, and micro-plastics with varying concentrations of fluorides and chloramines. Whilst the majority of these chemicals are added to tap water to make this more suitable to drink and the others found due to high levels of pollution, this can be toxic for fish. Tap water can be particularly harmful to soft water fish such as Discus fish and Dwarf Cichlids.

Due to high levels of phosphate and nitrates, this can encourage algae to grow and thrive making it particularly hard to get rid of. Whilst low levels of phosphates are not harmful to humans this can cause problems in your aquarium even with lower levels.

If you keep or plan on keeping a Marine reef aquarium, tap water will cause you many problems with both your coral and fish. Trace amounts of copper and considerable amounts of TDS (total dissolved salts) can be toxic to your coral and fish. In tap water TDS will range around 250 ppm or possibly higher. The fish & coral would not be used to these sorts of levels within an aquarium as they would not be this high in the wild.

In contrast to tap water, RO water is free from all dissolved salts and other chemicals that could potentially harm your fish and coral. This is because of the RO process which causes harmful chemicals to be separated from the purified water without the hardness and pollution found in rainwater and tap water.

Limitations of RO Water

As with everything, there are limitations to using RO water. The main drawback of using RO water in your fish tank would be that it is too pure. This would mean it is stripped of any minerals which may help to support your aquarium species. However, this is easily fixable by treating the water with minerals and chemicals to support the aquarium.

For marine aquariums, you will require marine salt.

And for freshwater aquariums, this may be bacteria balls which would help to introduce needed bacteria into the tank; try using our Aquarium Bacteria Balls

Using RO water will have multiple benefits on your aquarium. By using purified water you can ensure you will not be adding unwanted minerals and salts to your aquarium.

For more information make sure to have a look at all the articles on our Fishkeeping Advice page.