Reverse osmosis vs distilled water aquarium

Before getting a reverse osmosis system for your aquarium, it is important to know the difference between reverse osmosis and distilled water. I am sure the process should be familiar to most but I am talking more on the effect of each type of water on fish or reef aquariums. If you are currently deciding on what to use, the following will be very relevant


#1: Amount of impurities

One of the biggest difference between reverse osmosis vs distilled water is the degree of filtration. Reverse osmosis is the more powerful filter system among the two and is able to remove nearly all forms of sediments such that it contains almost pure H20. Distilled water, on the other  hand, is not so straight forward.

In theory, the purest of distilled should have nothing else but pure h2o.  This is why we always used distilled water in chemistry lessons. Unfortunately, not all the distilled water in the market is that pure as it depends on the grade. Most of the distilled water sold in groceries store are lower grade versions.  A lower grade distilled water is without chlorine but will still contain most other chemicals. The one chemical we want to avoid is copper as this is deadly to our fishes. Seen under this perspective, unless you are getting lab grade distilled water, reverse water is definitely better for your aquarium.


#2: PH level

RO water tend to be more acidic so their PH levels will not stay at the 7 level. It is advisable that you used a bit of tap water with RO water to balance the PH. Alternatively, you can add a remineralization filter to add back a couple of healthy chemicals which can also balance the water’s PH.

Distilled water tend to have a more balance PH.


#3: Make your own

In the long run, buying either distilled or RO water regularly is expensive. I prefer making my own as it is cheaper. As such, reverse osmosis water again has an advantage here. Currently, you can easily buy reverse osmosis system for home use easily. Be it one of these countertop reverse osmosis system that doesn’t need much space but has a slower water fill rate or the more expensive under sink Ro system which generates more water but need plumbing expertise, you have many option to DIY RO water.

In contrast, getting your own distilled water is tough, especially if you are talking about lab quality distilled water. In this case, you do not have much choice except to buy continuously from the grocery store.



At the end of the day, you can do well with your aquarium regardless of which type of water you used. There have been many cases of distilled water users reporting beautiful fishes or reef in forums online. Using reverse osmosis water might improve your current results or make things easier but it is not the most critical decision when it comes to setting up your aquarium.




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