How to Remineralize RO Water for Aquarium – Ultimate Guide

RO water is great for reducing unwanted chemicals in our tap water or to make it ‘less hard’.

Unfortunately, the side effect of RO is having all the minerals being stripped away, even those that are desirable for our aquatic plants, shrimps and fishes.

In this article, you will learn how to remineralize RO water to improve its mineral composition.

In particular, you will learn:

  • Step by step guide on how to do remineralization
  • Whether to use a commercial solution or DIY
  • What off the shelf products are recommended for remineralising your aquarium water


Why do you need to remineralize RO water

Aquarium plants need minerals like all plants. (For a complete list of minerals that plants need, refer to this wiki article: However, the RO process removes all minerals from the water, even those are needed.

Good news is most of them can be added to the RO water via plant fertilizers. However they do not contain some of the important minerals that are critical to plants:

  • Calcium
  • Magnesium
  • Sulfur
  • Cholorine

For these minerals, you will need to add them back manually, on top on any plant fertilizers that you are already using.


Step by step on how to remineralize your RO water

Here is how you actually remineralize your water. The following assumes you have already added in plant fertilizers. .


Step #1: Prepare the mineral mix that has calcium and magnesium

There are 2 ways of doing this:

Method One – Buy an existing and proven product like the Seachem Equilibrium and add them to the tank.  This will balance out the mineral content of your tank, in particular reintroducing calcium and magnesium into the water. There is no chlorine though so you might need to add salt tablets if you want it in your water. 

Method Two: Mix your own.  For those who think commercial solutions are too expensive or are not trustworthy, here is how you can DYI your own solutions. Important thing is to have the following:

  • Calcium Sulfate (gypsum)
  • Magnesium Sulfate (Epsom salt)

You can mix them in the ratio of is 4:1 (calcium sulfate to magnesium sulfate).


Step #2: Determine how much mix per gallon of water

Introduce the mix into a gallon of your tank water and monitor the GH.

Ideally, your tank’s water should have between 4 and 6 GH. Anything below 4 GH has the danger of failed molts.

Some shrimps such as Bee or Tiger shrimps can survive below 4 GH since they live in softer waters pretty well. For breeds like Cherry Shrimps, a below 4 GH water might cause molts to fail.

When the ideal target is reached, that is the amount of mix that should be introduced into your tank per gallon.


Step #3: Monitor the readings carefully

Once the mixed has been added, you need to keep a close eye on some key perimeters, such as TDS reading, GH levels, PH levels etc. Remineralizing is like a chemical process. A small wrong dosage can cause huge chain reactions in the tank.

Hence, despite doing step 2, we still need to monitor the readings of the tank when we first do the remineralization.


The advantage of buying a premixed vs DIY

One point that needs further explaination is the 2 methods that are discussed in step 1 above.

Although it sounds easy on paper, doing your own mix is very tricky. This is because trying to adjust one perimeter, say the Gh, while hoping the other perimeters remain stable is a dream. Usually, one mineral can affect multiple perimeters. To have the right mix, you need lots of experiments and might still not get it right.

For beginners, my advice is to go for commercial products such as the Seachem Equilibrium or the Salty Shrimp. Both have been tested by the companies and customers so they are definitely more reliable than your own DIY mix.


Seachem Equilibrium vs the Salty Shrimp

If you decided to buy commercial solutions for your remineralization problems, then the next question is which brand is better. Here is a quick comparison among my favorite two brands along different dimensions:

  • Price: Seachem Equilibrium is much cheaper. It costs around $1.90 per 100 grams while the Salty Shrimp is around $9. This around 4 times difference!
  • Color Change: Using the Seachem Equilibrium will change the color of your water to slight brownish, depending on your dosage. This is due to the iron present in the mixture. Salty Shrimp doesn’t have iron in their product.
  • Higher TDS and GH:  For the same quantity that I tested, Salty Shrimp usually result in lower TDS and GH reading. Whether that is good or bad will depend on your context. If you simply want to drive these readings up, it is cheaper to do so with Seachem Equilibrium. However, if your shrimps are sensitive to TDS or GH changes, then Salty Shrimp might be a better option.
  • Incomplete dissolution: The Salty Shrimp dissolves much faster and more completely than Seachem Equilibrium. In fact, Ialways could not get the latter to completely dissolve, resulting in a brown sludge at the bottom of the tank. Maybe it is my composition that is wrong or Equilibrium is just harder to dissolve properly.


A cheaper alternative to consider

Before even getting into this whole remineralization process, you need to ask if your water is really that hard. By hard, I mean a TDS reading of 500 and above. If not, there is an easy solution.

You simply mixed your tap and RO water to achieve an ideal TDS and GH level. You need to play around with the composition but it is possible to achieve a proper water quality simply by mixing the two.

This method, of course, applies to folks whose tap water is not like liquid rock. If it is, then what I said earlier still applies.



Adding minerals back to RO water is a must for a healthy shrimp tank. Even if you are not using RO water, it is still good to learn remineralization as some of your tap water might be too soft and needs to increase its GH for breeds like cherry shrimp.

Regardless of the reason, this guide has hopefully help you to understand how the remineralization process works and how do you go about doing it.

1 comment / Add your comment below

Leave a Reply

Your email address will not be published. Required fields are marked *