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The Shrimp Farm, Aquariums  Dealers, Bloomington, IL



Understanding Carbonate Hardness (KH)

Understanding Carbonate Hardness (KH)


In your aquarium you have what is called Carbonate Hardness otherwise referred to as KH. KH is something that does not play a direct role in shrimp health however it should not be taken lightly by any means. KH directly plays a role in your aquariums pH levels.

You might be wondering why we refer to it as KH when the initials are clearly CH for Carbonate Hardness, this would be because the “K” in kH is from a German word Karbonate and Karbonate is the measurement of bicarbonate and carbonate ions in your water.  Those ions are what helps keep your aquarium’s pH levels from going up and down. The ions hold the pH levels or reinforce them to keep from large changes in levels. When keeping aquarium shrimp or fish pH staying at a constant consistent level is key to their health. The measurement of KH is done by degrees and 1 degree being 17.9 parts per million (PPM). The higher degrees you water measures the more concentrated kH your water has.

In the shrimp hobby, shrimp are often kept with plants. Planted tanks often fluctuate in pH levels, if there is no kH present in the water. This is because plants take in co2 and release oxygen which is a key factor in raising the pH level and lowering it. During the day plants take in co2 or aka when you light turns on. While doing this the plants are raising the level of pH, simply because co2 molecules will attach themselves to your water molecules and produce a carbonic acid, the more carbonic acid the lower the pH. However since the plants are taking this molecule in, (because it is day time and your lights are on) they are raising the pH level. Once the lights go off plants stop taking in co2 and this causes your pH to increase! Make sense?


Lights on > Plants hungry > plants take co2 from water > less co2 in water means higher pH

Lights off > Plants not hungry > plants stop taking co2 from water > More co2 in water means lower pH

pH stock is something that is a killer of shrimp and fish. KH acts as the buffer to keep the pH levels of the tank to hold constant or at least stop them from taking huge dips up or down. In your normal aquarium KH levels can fluctuate for a few different reasons. When adding water to your tank with a higher KH level your natural level will rise, or if adding water with low KH your KH will naturally lower. This could be done by adding water after your water changes.

KH vs GH

KH and General Hardness (GH) are often thought of as one in the same. However they are not really related at all. GH is a measurement of Calcium and magnesium and other dissolved minerals in your water. KH is not this at all, it should be thought of as a buffer to hold PH constant. KH and GH will not always be the same degree, there will not be one always greater than the other either. In some cases you can find GH that is much higher than KH and in some cases you will find KH that is much higher than GH. A comparison between the two really doesn’t mean much at all, they are not related.

When testing your water for KH it is important to have a reading higher than 1. Anything lower usually is not good as this is your buffer and you want enough of it to hold PH at a level you desire for your shrimp or fish.

I personally use API GH and KH test tube kits to measure my tank levels. I have found this product to be the most reliable on the market.

“Keep on Shrimpin”


"America's Favorite Shrimp Guy"

Ryan Curtis

4 thoughts on “Understanding Carbonate Hardness (KH)”

  • Pepi

    Hi, you need to proof read your articles. There are contradictions around co2 and ph levels. Also the grammar could flow a lot better with some refinement.

    Still, very informative, thank you.

  • Richard pulman

    Hi Ryan just read your article and found it very easy to understand and informative, no doubt like me it as helped lots of people understand KH/GH values.
    Thanks for taking the time to compile this article
    Thanks Richie

  • Shae

    Hey! Just wanted to let you know your first paragraph doesn’t make sense. There’s a whole lot of increases in those sentences :). Otherwise good

  • tim

    Hello Ryan,
    Ryan I found that since I dose CO2...I actually have the timer come on and off through out the night to keep my pH steady...since I am dosing at levels that result in CO2 in the water at higher levels than what would be in equilibrium with the air...the CO2 degasses during the evening and my pH would rise...
    I also run my tanks with pretty much zero KH (amazon biotope tanks) and the shrimp are breeding quite frequently....
    Your article is one of the better ones I have read regarding KH and pH. One edit, 3rd paragraph near the end, you state the plants stop utilizing CO2 and this makes your pH increase....which you correctly restate later that it should make your pH decrease.

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