Water Hardness
Introduction
On this article you will learn about:
- How to Measure your aquarium’s Water Hardness, KH and GH.
- Steps to Reduce your aquarium’s Water Hardness, KH and GH.
- How to Raise your aquarium’s Water Hardness, KH and GH.
- What is GH in the Aquarium’s world?
- What is KH?
- What is the Difference between GH and KH
Stay with us to Finally Understand these Terms (and give lessons if you wish 🙂 .
Table of Content
Aquarium Water Hardness KH and GH
Contrary to what you might think, you can manipulate and adjust your water hardness.
“I am from Florida, and my Tap Water is very hard.
Because I wanted some non-hard water fish in my tank, I had to Reduce and Keep it at about 14 dGH.
This Article helped me a lot.”
The Best Way to Test & Measure your Aquarium’s Water Hardness, both GH and KH, is using this API Test Kit.
Watch this Step-by-Step on How To Use this Test Kit:
Water Hardness is measured in:
- Degrees GH for the “General Hardness” (how much magnesium and calcium you have in your tank water)
- Degrees KH for the “Carbonate Hardness” or “Total Alkalinity” or “Buffering Capacity” (how much carbonate and bicarbonate ions you have in your tank water).
Difference Between KH and GH
The difference between KH and GH is that KH measures carbonate hardness (CO3 and HCO3), and GH measures Calcium and Magnesium (Ca and Mg).
You can have a high KH and low GH or vice versa.
They are definitively different things.
It’s common and acceptable to say I have “hard water” or “my water is soft” which usually means that both GH and KH are high or low, but to be more precise, we should always specify GH and KH values separately.
When it’s mentioned that a fish or plant requires “Soft Water,” it generally means they prefer low KH and low GH.
As said before, KH measures your aquarium’s water carbonate hardness.
A satisfactory water KH level protects your fish, snails, and shrimp against sudden pH fluctuations that could cause their death (pH crash).
GH (General hardness) measures the number of dissolved calcium and magnesium ions.
An adequate Water GH level is essential for the growth of certain fish species, invertebrates, and plants. It helps their muscle development, organ function, and breeding of certain fish species.
Water Hardness KH GH frequent questions and answers
What is the ideal GH General Hardness level for a freshwater aquarium?
In general, the ideal GH / General Hardness’s water level is between 3 to 15 degrees dGH.
Different fish, plants, and invertebrates have different needs. Read More here
Don’t forget to learn more about pH and Ammonia as they can also kill your fish! Read More Here.
What is the ideal GH General Hardness for a planted aquarium?
For Planted Tanks, and to promote Faster Plant Growth, the ideal GH / General Hardness is between 3 to 5 degrees dGH.
What is the ideal KH for a freshwater aquarium?
In general, the ideal KH’s water level is between 4 to 12 degrees dKH.
Different fish, plants, and invertebrates have different KH needs. Lear more here.
Looking for a KH’s Scale table? Check here.
What is the ideal KH for a planted aquarium?
For Planted Tanks, and to promote faster Plant’s growth, keep your KH’s level between 4 to 7 degrees dKH.
Is high KH bad for fish?
Generally speaking, a higher KH is indirectly good for fish, invertebrates, and plants as it reduces the risk of fast pH variations, called pH crash, which can be very dangerous – Read More here.
Certain fish species prefer low, medium, or high KH, so you should always research before changing your KH level or buying new fish.
How to reduce the KH and GH hardness (Hard Water or Water Hardness) in a freshwater aquarium?
To reduce your aquarium’s water KH and GH levels, you can use:
- Water Softener Pillows (like this one)
- Distilled Water or RO Water during your Water Changes or Initial Setup.
Read more about these two methods here.
Attention, if you are trying to reduce your aquarium’s water hardness but it keeps raising, read this article.
Watch this video to see how a Water Softener Pillow works.
How to raise KH and GH hardness (Hard Water or Water Hardness) in a freshwater aquarium?
To raise your aquarium’s water KH and GH in an easier and more controlled way, you should use Alkaline buffers.
Alkaline Buffers are safe and you can easily reach the KH or GH desired levels as they come with detailed instructions about how much you should use to raise 1 or 2 or 3 degrees.
Read more about these options here
How to convert from dGH to ppm
Most water test kits give you the result in dGH, and sometimes you want to know the value in ppm.
To convert it, multiply the dGH number by 17.9 to obtain the equivalent ppm.
For example: If you have 2 dGH, multiply 2 by 17.9 , which is 35.8 so 2 dGH is the same as 35.8 ppm
A much more efficient way is to use our online dGH to ppm calculator.
Just type the value and press Submit.
If your Aquarium’s Water Hardness is high and you want to reduce it, read our how to here.
If your Aquarium’s Water Hardness low and you want to raise it, read more here.
How to convert from ppm to dGH
Sometimes you want to convert your water hardness level from ppm to dGH.
In this case, divide the ppm number by 17.9 to obtain the equivalent in dGH.
For example: if you have 35.8 ppm and you want to know this number in dGH you should divide 35.8 by 17.9 and you will find 2. So 35.8 ppm is the same as 2 dGH.
A much more efficient way is to use our online ppm to dGH calculator.
It is high? Learn how to reduce here.
Is it low? Do you want to raise it? Check how to here.
General Hardness (GH)
Measuring your aquarium water’s GH means measuring the amount of calcium (Ca++) and magnesium (Mg++) ions in the water.
GH is essential for fish, plants and invertebrate’s development, organ function, and breeding.
Do you want to know the difference between GH and KH? Here.
In general, 3 to 15 dGH is the recommended GH level, but if you are working on a Planted Tank, 3 to 5 degrees dGH is a GH good level.
Some important notes:
- Shrimp are especially sensitive to GH levels.
- Cichlids and livebearers, for example, prefer hard water.
- Aquatic Plants benefit from calcium and magnesium dissolved in your water, this means higher GH levels are important for their growth.
Most water test kits give you the result in dGH, and sometimes you want to know the value in ppm.
To easily convert it, multiply the dGH number by 17.9 to obtain the equivalent ppm.
For example: If you have 2 dGH, multiply 2 by 17.9 which is 35.8 so 2 dGH is the same as 35.8 ppm
You can also use our Online dGH to ppm calculator that is right below.
Sometimes you want to convert your GH Water Hardness level from ppm to dGH. Divide the ppm number by 17.9 to obtain the equivalent in dGH.
Be more efficient and use our Online dGH to ppm calculator that is right below.
What is the difference between GH and dGH units of measurement?
Some Water Test Kits or Articles can quote a Water GH’s level in GH units or dGH units (dGH stands for degree GH).
Think like if you are measuring something in foot or feet, in meters or kilometers.
The typical unit found on websites and in the literature is degrees of general hardness (dGH,).
How to convert from dGH to GH?
To convert from dGH to GH, you can use this online calculator.
How to convert from GH to dGH?
Here you have the opposite conversion online calculator to help you to convert from GH to dGH.
Total Alkalinity (KH)
What is KH? Why it is so important?
KH is a water property defined by the quantity of bicarbonates, carbonates, and hydroxides dissolved in it.
If your aquarium’s water has a lot of bicarbonates, carbonates, and hydroxides, then your water has a high KH.
KH is essential and should be monitored due to its capacity to neutralize acid components.
As an example, if you throw an acid substance on your tank water, these bicarbonates, carbonates, and hydroxides will react with it and will neutralize an amount of the acid component avoiding the acidification of your aquarium water.
Why is this important?
Let’s say you are refilling your tank with TAP water, and this water is very acid, or maybe you found a beautiful rock, and you add it to your tank, but you didn’t know it has a lot of minerals that turn the water more acidic.
If you have a good level of KH, all those carbonates will react with the acid component, neutralizing it and avoiding a drastic pH variation (pH crash) which could kill your fish.
This is why the KH of your water is also called the buffering capacity.
This property is crucial because it helps to avoid fast changes in the water pH, which is not good for fish.
Do you want to know the difference between GH and KH? Here.
The “U.S. Department of the Interior has a good article about KH“.
Having a good KH level means that you can keep your pH level fairly stable.
So, in resume, having a good level of KH helps to protect against dangerous pH fluctuations (pH crash).
In general, try to keep your KH between 120 and 180 ppm (4 to 12 dKH)
How to measure water hardness.
The best way to measure your aquarium water hardness is using a test kit like this one.
Test kits are available at Amazon or pet stores and can be purchased for as little as $15.
They are an excellent way to test your water hardness.
These kits are easy to use and come with clear instructions.
Watch this Step-by-Step video.
How to reduce Water Hardness.
There are many ways to reduce your aquarium’s water hardness, but we are going to discuss the 3 most common ways.
- Reverse Osmosis system
- Distilled Water
- Water Softener Pillows
The two most common ones are using a Reverse Osmosis system and
Attention, if you are trying to reduce your aquarium’s water hardness but it keeps raising, read this article.
Reverse Osmosis system
Reverse Osmosis systems are a group of filters that remove all traces of minerals from tap water. You can use RO water when making your aquarium or during water changes. You can buy RO water in most of the local fish stores or you can buy your own system. I like to use this RO kit from AquaticLife – it costs about ($70).
RO water will slowly reduce your GH and KH in the same time.
Distilled Water
Distilled Water can also be used.
You can buy small quantities in Walmart or other grocery stores. See this link for an example.
Check its pH before you use it and adjust accordingly.
You can use it during water changes or when building your tank.
Distilled water will slowly reduce your GH and KH in the same time.
Water Softener Pillows
You can use water softener pillows to reduce your GH.
They are resin bags that remove Calcium, Magnesium, and Soluble Heavy Metals, including Iron and Copper. They don’t add harmful chemicals to your water.
This is the one I have used before.
Attention: they work very fast!
Check your GH daily or even twice daily while using them so you can remove the pillow when you reach the desired level.
Watch this video to see how the water softener pillow works
How to raise your KH Water Hardness
The most safe and controlled way to raise your aquarium KH hardness is using a chemical from Seachem called Alkaline Buffer.
We like to use this product because you can reach exactly the level of KH you want.
This product instruction will come with a table where you can check the size of your aquarium, the desired KH level and how much you should use. It tells you how much you should use to increase, for example, 1 unit of your KH. It’s easy to understand and use.
It is safe and work well.
How to raise your GH General Water Hardness
The most safe and controlled way to raise your aquarium GH hardness is using a chemical from Seachem called Equilibrium.
We like to use this product because you can reach exactly the level of GH you want.
This product instruction will come with a table where you can check the size of your aquarium, the desired GH level and how much you should use.
Their directions tell you how much you should use to increase, for example, 1 unit of your hardness. It’s easy to understand and use.
It is safe and work well.
How to know which water my fish need?
You will need to do some research on Google but I can guide you on the steps.
- Open Google (www.google.com)
- Type something like “abcdef and fish and types of waters” replacing the “abcdef” with your fish name.
Like here, for example
Open the page and look for something saying the pH this fish needs, temperature, and also Water Hardness.
See this example:
I suggest you research at least two sites.
Conclusion
Your Aquarium Water GH and KH levels are essential factors in determining the health of fish and plants.
You should always know the GH and KH of your tank when buying fish or invertebrates, and double-check if they are compatible.
Choose your livestock based on your water
Or choose you livestock, and adjust your water accordingly.
If you live in the United States and if you want to know how is your TAP Water, our USGS has a very good page with a lot of good information (here).
References
For this article, I used the “USGS – Water Science School website“, “Aquarium Water Quality: Total Alkalinity and Hardness from FDACS – Florida Department of Agriculture” and also my 12 years of experience with fresh water tanks.
U.S. Department of the Interior Credit: James M. Omernik, Glenn E. Griffith, Jeffrey T. Irish, and Colleen B. Johnson
Aquarium Science Org here.
What is Next
I suggest you to have a look in my “Water Parameters” article to learn about pH, Ammonia, Nitrites, Nitrates and much more. Click here.
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