Using GH/KH Hardness Test Kits in Brewing

GH and KH Test Kit

Adapted from

A simple water tool for the brewery can be home water testing kits popularly used to manage aquarium water. In particular, titration kits that measure both GH or General Hardness and KH or Carbonate Hardness are preferred over the less useful test strips.

The Procedure:

A water sample is drawn and placed into a rinsed test tube. Careful measurement is needed, and the test parameters are set for 5 ml of water. You should let the water run just a bit to ensure that you are getting a good sample, and not one that has been sitting in the pipes for a period of time. You can also pull samples post filters or softeners, but for the brewery – you want a sample that is closest to what you will pull for hot liquor. An eye dropper or pipette can help with precision, but I am typically looking for confirmation – and not trying to target a very precise number.

With the test tube filled to the 5 ml mark, add a single drop of test solution, cap and shake. Repeat this process iteratively, counting each drop, until the solution suddenly changes color. Convert the number of drops required into the hardness value, and convert that value then into the appropriate useable value. This is the same procedure for GH and KH.

With this kit, 1 drop of KH test solution in 5 ml water = 1 (dH) hardness which equals: 17.8 ppm alkalinity as CaCO3.  Given the very small volume, the resolution of the kit is not very granular.

1 drop of GH test solution in 5 ml water = 1 (dH) hardness which equals approximately 7.1 ppm Calcium concentration or adjusted (Kai) to 5 ppm Ca and 1.3 ppm Mg.

To Increase Testing Resolution:

20 ml solution with stirbar

The procedure is essentially the same, with the change to a larger vessel. I like to use a 50 ml flask, filled to 20 ml, and use a stir bar. Once the volume is precisely measured, I place this on a stir plate and set the bar spinning very slowly. Note the volume is established without the stir bar. Then add single drops into the solution slowly, counting iteratively, until the color changes. This increases the resolution by diluting the effective solution of each drop, so you can do the math if you want more or less resolution. I would start with the normal test, then move to the appropriate resolution should that may be required.

With this procedure, 1 drop of KH test solution in 20 ml water = ¼ (dH) which equals: 4.45 ppm alkalinity as CaCO3.

1 drop of GH test solution in 20 ml water = ¼ (dH) which equals approximately 1.78 ppm Calcium or adjusted (Kai) to 1.25 ppm Ca and 0.33 ppm Mg.

This allows me to measure very accurately the residual carbonate of my water, and determine generally when my RO filter is most efficient. By taking periodic samples during filtering, the goal is to have the fewest possible drops added into the solution. By plugging the resulting numbers into Bru’n Water, Kai’s Water Calculator or Brewer’s Friend, I can also make a more accurate assumption of the alkalinity of the hot liquor and subsequent potential acid required to determine mash pH.

Bru’n Water converts degrees GH into a calcium number, and degrees KH into bicarbonate. You can find this on the Water Report Input sheet and you can use these numbers to generally check against an independent lab report. Useful also to determine how much your water changes over the year. If you see a very large discrepancy, say more than 15%-20%, then time for a new report and analysis.

Kai’s Water Calculator, using the “simple water test” makes some assumption on GH, passing roughly 30% to magnesium and the rest toward calcium. It also converts KH into figures for alkalinity as ppm as CaCO3 and Residual Alkalinity in ppm as CaCO3. This appears to be discrepancy compared to Bru’n Water spreadsheet, however both result in very close predictions when used correctly. I believe that some of Kai’s Water Calculator has made it into the Brewer’s Friend web tools for water.

KH and GH Goals:

To keep things simple, I use KH to determine alkalinity and GH to check my flavor ion concentrations. Determining the right place to be for liquor alkalinity really varies based on your goals, and the beer that you are creating. Dark beers require more alkalinity than pale beers to offset the acidity of the dark crystal and roast malts. A general goal should be somewhere less than 50 ppm alkalinity, a bit over for  a dark beer, and a little under for a pale beer. Also consider dilution strategies or water treatments such as lime softening to reduce alkalinity.

GH goals are really focused on calcium salt additions, which include flavor ions, and highly variable based on your goals with a given recipe. With RO water, I expect nearly zero GH, until I make additions. My water is very full of bicarbonate and sodium, and the filter is fairly effective at removing that. The General Hardness test is a good check on my technique of adding minerals. I can determine quickly if I have misapplied my gypsum, Epsom and calcium chloride additions, however I use the test very seldom.

On the carbonate side however, a RO filter becomes more efficient as it is used, meaning if I have not brewed in a few weeks, then I need to let it run for a while before drawing the hot liquor volume. Using this test, I have determined the correct amount of time, taking small samples every minute, is about 5 minutes at 60 psi, or about 5 gallons. I use this water to prepare Star San and then fill the HLT. This allows me complete control over the quality of my source water and the gram weight of the additions. Because I have so little alkalinity and hardness, I must be very careful estimating my acid and alkaline additions to the water. There is no buffering to forgive a small error!

You might note that I am not discussing Residual Alkalinity. RA can be estimated by taking both readings and plugging into the following formula. You can use either dH or “ppm as CaCO3”.

RA = KH – GH / 4

RA is a less useful tool when using RO water as a source, and often a negative RA number is present that is very confusing.

Kai’s instructions are much more specific in how to apply the values.


A simple water test is not a replacement for a true analytical report on your brewing water source. Assuming your report is very good, it can be a tool to measure variability and troubleshooting alkalinity issues in the mash. The GH test can also help you to verify, roughly, your salt additions, and when combined with other tests, such as water pH and TDS, useful if you need an additional check in your process. As mentioned, in my brew house, it has helped me to optimize my liquor collection procedures and ensure that I am betting the best filtered water from my RO system. I can see it being useful for store bought RO water sources, or checking potential new sources of water. It is very easy to conduct and the results are virtually instant.

The most important test I find useful is the alkalinity or KH test. Understanding and managing your mash pH, which is a direct function of the alkalinity of the mash liquor is incredibly important and has the largest flavor and extraction contribution to your beer.

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