# Please help with calculating GH



## johnzhou2476 (Nov 28, 2006)

Please help me calculate my GH given these water parameters:

I’m embarrassed to say that after so many years in this hobby, I still can’t figure out how to calculate my GH. 

Here are my water parameters:
• Calcium 10ppm 
• Magnesium 4ppm
• Nitrate 9ppm
• Potassium 16ppm

I know GH only factors in Calcium and Magnesium level. But, if that’s the case isn’t that a poor indicator of true water quality? What if my Potassium level and Sulfate level are off the roof, like over 200ppm of each? Should GH and TDS reading be used in conjunction to get a true picture of your water parameter? I feel that GH is often over emphasized while TDS is neglected. BTW, my TDS meter reads 140 – does that sound about right given what I have above and using mostly RO/DI water or do I need to get it recalibrated? 

I know KH is a function of GH and that the two are interconnected. So, If I have 2 degree of KH, does that mean I need that add that to my GH – I’m confused? 

Lastly, can someone please confirm that 1 teaspoon of Calcium Carbonate raises approx. 1 degree of GH and 1 degree of KH to 25 gallon of water? 

THANKS A MILLIION!


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## ashappard (Jun 3, 2006)

TDS can be good to watch between water changes, as it accounts for the sum of many things and creeps up as you dose. I see GH as less a function of water quality than water hardness, still I do not measure it.

I use a simpler approach, when I do a water change I add an amount of GH booster to bring up the GH of the water _added_ by an estimated 3degrees. So I add 4 grams per 5 gallons of RODI water. Its not precise, but it allows the Ca/Mg to be available in the proper ratio and that has been enough in my experience with what I keep. Its also convenient in that when I do a water change and then add GH booster, I measure TDS and see that it is about in the same place as the last water change. If not, I change a little more water.

There is a lot of K in the booster I use - its patterned off Equilibrium. Someone correct me if this is wrong, but I think the K has the most significant effect on TDS.

I can't say that KH and GH are not interrelated, but I do know that you can have one without the other and manage them separately. For example, I aim for 0KH and 3-4GH. Sorry I cant answer your CaCO3 question, I havent used that one in quite a while. I do remember it being rather hard to dissolve and had to let it sit for a long time in water before adding it to the tank.


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## Diana K (Dec 20, 2007)

GH is a measure of Ca and Mg. 
KH is a measure of carbonates. Carbonates act as a buffer that tends to stabilize the pH on the alkaline side of neutral.

Here is the relationship:
In natural systems the rain or snow falls on rocks and dissolves some of the rock on its way to the river. If the rock is high in a particular mineral then the water might be too. Some rocks do not dissolve very well. 
Various forms of limestone dissolve pretty well. (some do not) Limestone is mostly Calcium Carbonates and Magnesium Carbonates. Therefor, when water flows through soil or across rock that is high in limestone the water will pick up both Ca, Mg andcarbonates, and most often the pH will rise. The rock will gradually dissolve leaving caves, Karst landscapes and rocks with holes. 

In high rainfall areas there are a lot of plants that do not let the rain hit the soil, and the rain and plants have long ago removed most of the minerals that might have dissolved in the water. This is part of the reason that rain forest river systems have very soft water, low in both carbonates and most minerals.

In areas with less rainfall there are fewer plants so that rain will run off through the soil, and there are still minerals that can be dissolved. This is part of the reason that the Rift lakes, the Great Salt Lake and many other inland bodies of water are very hard and alkaline. The water evaporates from these waters, too, leaving behind the minerals, which is another reason that rain forest rivers tend to be softer and lakes in slightly drier areas tend to have harder water.

There is enough variation in this that when you research fish or plants for your tanks you do want to look into the optimum water parameters and try to stay similar to them, and not mix fish from widely different water chemistries. 

Now, back to aquariums:
I test GH, KH, pH, salinity (certain tanks) and TDS. 
I do not test the individual minerals that you list. 
Most of my tanks have similar enough readings that I can call them:
"Soft Water" tanks. Tap water (GH and KH are roughly 4-5 degrees), I add plant fertilizers in small amounts. I have peat moss in several of these tanks, and Soil Master Select Substrate which has removed the KH down to 0 but not touched the GH. I add baking soda when the KH drops, and raise it back up to around 2-3 degrees. TDS is slightly higher than the tap water. 

"Hard Water" Lake Tanganyika, Guppy tanks and other livebearers. There is some variation in these, not all are as extreme as Lake Tang, but they do have added minerals to raise the GH and KH. No sodium chloride. TDS is a LOT higher than the tap water. 
Seachem Equilibrium or Barr's GH booster. These products are high in K, Ca, Mg, Fe and Mn (if I remember, no container in front of me). This product does nothing for KH, or pH. 
Baking soda for carbonates. This also results in a higher pH.

"Brackish Water" I add the salt and mineral blend for marine tanks (Coralife). GH and KH are off the scale, and TDS is highest of all. Specific gravity shows 1.004, and the salinity test agrees that most of this is actually sodium chloride. 

1 teaspoon of baking soda added to a 29 gallon tank raises the KH by 2 German degrees of hardness, and the pH from 6.0 to 6.2. Other things certainly may affect the pH when the KH is this low. I also have peat moss in most of the tanks with Soil Master Select. 

Calcium Carbonate may or may not dissolve very well in your water. You will have to get a sample and test it, if this is what you feel your fish and plants need. I would set up a measured amount in a 5 gallon bucket and run a small pump or bubbler and test every few days for a week or longer. You might find that it doe snot dissolve right away, but will dissolve over time. Roughly a week is reasonable to test, if you are doing weekly water changes then you will have some idea how this material may behave in your aquarium. 

Seachem Equilibrium has the values on the label, and it is also a good idea to run a similar test using your own tap (or other source) water. This is a bit tricky to dissolve in my tap water, I need to shake it up in a small amount of water, then run the water prep barrel for several hours. Dissolves best in hot water.


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