A couple of years ago, we published a method for making your own water recipes, using concentrated mineral solutions, diluted with deionised water, to make a range of waters with different hardness and alkalinity. This post updates this, with new recipes that allow you to easily target a specific GH and KH in your water.

We’ve also added in a calculator that allows you to work out what will happen if you add minerals to existing water, rather than just deionised water. This will be useful to anyone in soft water areas who would like to remineralise their tap water, for example.


The Recipes

You’ll need the following before you start:

  • Baking Soda – NaHCO3, Sodium Bicarbonate (not to be confused with baking powder)
  • Epsom Salts – MgSO4.7H2O, Magnesium Sulphate.¹
  • Deionised/Distilled/Ultra-pure water
  • Scales (accurate to 0.01g)
  • 3 x ~1L water containers (preferably glass, and odour/residue free)

The Buffer Solution

Dissolve 1.68g of sodium bicarbonate in 1L of deionised water. This creates a solution with a KH (as CaCO3) as close as we can get to 1000ppm.

The Hardness Solution

Dissolve 2.39g of Epsom salts in 1L of deionised water. This creates a solution with a GH (as CaCO3) of 1000 ppm.


Create Your own Water Recipe using Deionised water

Using these two solutions with deionised water is very simple. To get your desired KH and GH, you can simply use that number of mls of each solution, then make the total volume up to 1L with deionised water.


Mineralise Pre-existing Water

If you prefer to add hardness or buffer to existing water, perhaps to take advantage of the calcium or other minerals already in the water, then you can use this calculator to work out what the final KH, GH, and TDS of your water will be. This is helpful if just want to boost the hardness of your favourite bottled water, for example, or to mineralise your tap water if you live in a soft water area.

To use this calculator, measure the KH and GH of your existing water (and optionally your TDS), then put these numbers into the calculator along with the amounts of each solution you plan to use.

You’ll see that adding 10ml of a solution doesn’t simply increase KH or GH by 10, like it does with distilled water. This is because the solutions themselves dilute the water that you started with. By tweaking the amounts of each solution that you use accordingly you should be able to work out what amount will get you your target GH and KH.


Why are these Recipes Different?

Our previous solutions were designed to give you 1g/L of magnesium or bicarbonate ions, respectively. However, this is not the way that we usually measure hardness and alkalinity.

Rather than give the concentration of the ions directly, both hardness (GH) and alkalinity (KH) are usually measured in calcium carbonate equivalents. In other words, it tells you how many parts per million of calcium carbonate you would have, if all the hardness or alkalinity was due to calcium carbonate alone.

It’s measured this way because simple drop test kits can’t distinguish between calcium or magnesium ions, so it’s easiest to assume it’s all calcium. This means that when we start using magnesium or sodium salts to tweak the water, we need to do a bit of maths to convert those amounts into CaCO3 equivalents.

To make it easier for you to experiment with different hardnesses, we’ve altered the recipes to aim for a specific KH and GH instead. This means that you can easily target any GH or KH you like, with no conversion required.


A Note about TDS

Note that the TDS given by this calculator might not be exactly the same as the TDS you would see if you measure the resulting solution with a TDS meter. This is because TDS meters assume a certain ratio of all the ions in the water, and by adding these solutions, we’re messing with that ratio.


A Plea for Mathematicians

It should be possible to set up a pair of simultaneous equations to work out exactly what amounts of each solution to use to reach a target KH and GH when working with pre-existing water. However, setting these equations up in a spreadsheet is beyond us here at BH! If any mathematician readers would like to help us solve this problem and create a more powerful calculator, then we’d love to hear from you.

¹ The “.7H2O” part refers to the fact that water forms an intrinsic part of the crystal form of this salt that you can buy in the shops, which is the clear crystals called Epsom Salts. Each magnesium sulphate molecule is surrounded by seven water molecules in this type of crystal. We’re specifying this here, as the weight of the water in the crystal affects the calculations.

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