How To Make Tap Water Safe For Saltwater Aquariums (RO DI)

Image by rony michaud from Pixabay
Image by rony michaud from Pixabay

How To Make Tap Water Safe For Saltwater Aquariums (RO DI)


Water is obviously the main component of any fish tank and that means you want to be making sure you are only putting in water that is safe for your aquarium.

There can be all sorts of expensive ways to get quality water for your tank from bottled water to RO DI water bought at your local pet store but how about just using tap water from your home to make the water changes? You can definitely do that and potentially save a ton of money in the process! However, there are a few things we should discuss before you begin filling your twenty-gallon tank with fresh tap water.

RO DI Filters To Make Tap Water Safe

5 Stage RO DI Filter

An excellent system if you don’t have chloramines in your tap water.

Replacement Filters

Replacement filter set for the 5-stage RO DI filter system.

Chloramine RO DI

6 stage RO DI system capable of removing chloramines from tap water.

Replacement Filters

Replacement filter set for the 6-stage RO DI filter system. You’ll also need a replacement RO membrane.

Can you use tap water in a saltwater aquarium?

In short, yes you can, but you want to know what the composition of your local water is so you can know best how to introduce it to your reef tank. Water is treated for human consumption and not for the fish in your reef tank. To have tap water that can be safely introduced to your fish, you need to treat it to remove some of these impurities that hurt marine life.

Issues with tap water

Tap water can be home to thousands of little problems for your reef aquarium. The water can be full of sediment and some of those harmful compounds that you work so hard to try to remove from your saltwater aquarium such as ammonia, nitrates, and chloramine. These elements will cause different problems for your tank stability and will adversely affect the health of your saltwater fish.

How can I make tap water safe for my aquarium?

You can help to make your tap water safe for marine life by treating it with the proper conditioner. However, this is not a full-proof method as the water might have other additives that are not covered by your conditioner entirely likeChloramine or the solids that might be in your water. The solids found in your water can lead to tank failure over time and that is something that we want to avoid.

 City water can be a mixed bag so you want to know what you are dealing with before you begin investing in ways to treat it. You want to call your city’s water treatment plant and ask how they treat their water and what additives might be in it. This will help to give you a better picture of what the water quality is life and how to best invest our money to treat it for your reef aquarium. Fair warning that sometimes there might be a charge associated with the testing but you can also try testing the water yourself if you have the proper test on hand.

It is best to invest in a RO DI unit for your saltwater aquarium as it will be the most convenient option over trying to treat the water with a conditioner over time. Plus, the units are not all that expensive when compared to other pieces of reef aquarium equipment.

Chloramine vs Chlorine

We know you were thinking it, but it turns out there is a distinction between chloramine and chlorine. Chlorine actually dissipates fairly quickly in water but when joined with ammonia, the chlorine and ammonia combination create chloramine which can stay in solutions much longer than standard chlorine. Therefore, city water treatment plants use them in the water supply to help keep tap water clean for human consumption but that also means that the compounds can get to your fish when using straight tap water.

However, it is not guaranteed that your city uses this method so always double-check by running your own tests or call your local treatment plant to determine if they use chlorine or chloramine in their process.

How to test for Chloramines

How to remove chloramine from water

  • Conditioner – The issue with the conditioner is that you need to have the correct conditioner that will work best for your local water. They come in a variety of combinations, but you are often better off sticking to the conditioners that can do it all so like a conditioner that helps remove ammonia, chloramines, chlorine from your water. You should have tests on hand thought to ensure that you are conditioning the water enough for your marine life.
  • RO DI – A good RO DI system will save you a lot of time and extra work if invested in early. You only want to make sure that your unit can cover the above compounds and will be able to keep up with the water levels of your tank and inhabitants. The filters on these systems do wear out so important to understand what the rate of wear is for your specific filter models.

Reverse Osmosis System for Saltwater Aquariums

A reverse osmosis deionization filtration unit (RO DI) is a system that allows hobbyists a lot more control over the quality of the water being added to their reef tank by removing the contaminants that are commonly found in city water supplies. RODI systems do this by first filtering out the dissolved solids in the water and then passes through another filter that helps to remove any of the other harmful chemicals that might damage the health of your aquarium.

Do you need RO DI water for a Saltwater Tank?

It is highly recommended that you use a RO DI system for your saltwater tank and that is because it helps to ensure that you will not have water quality issues as you perform water changes. Plus, conditioning water will take up time and will require that you are priced in your measurements and testing. It is also way more convenient than storing aquarium safe water. Of course, you can buy the water and store it but why not just have your own system and save yourself the extra leg work every couple of weeks? 

How many stages should my RO DI have?

This can be a tough question to answer as it can depend on what kind of saltwater aquarium you are cultivating, and the water supply you are pulling from. As discussed earlier it is best to do your research and ask your local water supplier what kind of processes their treatment plant uses and if you want to carry out your own experiment you can test the water yourself. Depending on the levels of contaminants in your water, this will determine how many stages your RO DI unit should have.

You should have no less than a 5 stage RO DI system but investing in systems with more stages will help significantly and make your tank a lot more stable in the long run. If you notice that you have higher than average levels of ammonia and other harmful compounds then it probably best to bite the bullet early and invest in a higher stage system.

What do the RO DI stages do?

The different stages are filters that help to act as additional membranes for water to pass through and in doing so each filter targets specific needs or in some cases acts as checks and balances on the other filters in case something wasn’t picked up the first time.

 Filters include a carbon block filter, sediment filter, DI resin filter, and an RO membrane. Larger units will have additional filters usually doubling up on resin filters and carbon block filters.

How to set up a reverse osmosis system for an aquarium

Setting up a RO Di unit is actually fairly straight forward compared to many other saltwater aquarium equipment pieces. If you have a sink with a lot of free space underneath for storage that would be best. You can also just install it whenever you need it since you only need this water for water changes for the most part. Depending on where specifically you install the RO DI, you may need to invest in other valves to help with the installation like if you are going for the more covert under the sink option.

  1. The product line (red line) should be placed on the faucet of the sink. Depending on the type of sink you are using you may need an adaptor for the specific sink you have. If you are using a standar4d sink chances are you will need to remove the tip of the faucet (the aerator) so that the diverter valve can fit on the faucet.
  2. Place the waste line (black line) into the drain of the sink.
  3. Product line (blue line) is what will disperse the water that can be used for your saltwater aquarium. You will want to ensure that this line has some spare jugs or buckets to collect the water. Make sure to always have clean storage containers as containers can collect gross microbes between use and putting your new clean water in those dirty containers would defeat the entire purpose of the RO DI.

How to set up an RO DI filter

Can you use distilled water in a saltwater fish tank?

If it is so much trouble to use tap water, can’t you just use distilled water for your saltwater tank? Yes, you can but also no, so let me explain. Distilled water is created by evaporating the liquid to become steam and collecting that steam as water once again. What is accomplished in the process is that the impurities in the water are mostly removed leaving mostly pure water. That sounds great on paper but as you know fish are picky creatures and require a lot more than simple distilled water. Think of the ocean or a lake.

Do those bodies of water have pure H2o in them? No, they are made of lots of different minerals that are beneficial to marine life. That doesn’t mean you can’t use distilled water at all in your tank, but it should be kept as a method of the top off rather than your main source of water. You can also use distilled water if you are properly re-mineralizing which requires that you are adding minerals like iron and calcium for your reef aquarium to thrive.

Final thoughts

Now that you know how best to use the tap water in your home you will hopefully save some time running around trying to collect water. Remember to always replace the filters on your RO DI regularly. You will want to check how long your specific filter lasts and keep some spares on hand. You should also keep manual tests on hand to check and see if your RO DI is working properly so as to avoid any disasters over time. You can never be too careful but if you follow the advice above you shouldn’t have any issues.

Be sure to check out some of the other articles on our site to learn more about saltwater parameters and how often you should be doing water changes.

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