# Just tested GH/KH, what do the results mean for my tanks?



## Argus (May 22, 2013)

See this post by Diana. 

I'm new to testing GH and KH so my understanding is based mostly on reading various sources. 

GH and KH should be close to each other in testing numbers.

Different fish have different KH requirements. Corys are supposed to like anything from 2-12, Angelfish 1-5. Rainbows 9-19, African Cichlids 10-15. I have angelfish doing very well in KH 6 and GH 7. Farm raised fish are supposedly more tolerant of different water conditions than wild caught fish. My angels are USA farm raised.

Most plants seem to like KH 4 to 8. Some like harder water, some softer. Best to look up the requirements for the plants you have. 

Your tap water seems to be in a good range at 6 & 7. Plants might have depleted the KH in some of your tanks. Water changes should help restore some of it.

If you want to adjust KH or GH:
Add Seachem Equilibrium to raise the GH
Add 



 to raise the KH. Baking soda will also work, but potassium bicarbonate is probably better for plants.


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## WaterLife (Jul 1, 2015)

Thanks for the info Argus.

So the carbonates and bicarbonates are carbon sources and plants would use them up?

In the 55 gallon hillstream tank, there is no plants and no algae at all (tank light died a months ago, haven't replaced yet, they get by with varied algae wafers/gel and vegetables), literally just fish, so I'm not sure why the KH is really low for that tank, but it has been 3-4 weeks since a water change on that tank, maybe that has something to do with that, does it deplete any other way, evaporation? or???
At least its good to hear it's easily increased.

But I don't get how the pH still remains at 7.4 with the KH being so low in some tanks. I was under the impression the pH and hardness levels are in similar relation to one another.
That is why I am wondering if my silica sand (silicates) has anything to do with any of this. How different are silicates from phosphates/phosphorus?
I will do all the tests again later today to double check values.


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## WaterLife (Jul 1, 2015)

Just posting my city water quality report to get any insight on the levels listed (and how it affects my fish and plants, human health too even) and if it helps make more sense of my pH, GH, KH test results, or further complicates things. I do not have a TDS meter currently. Does TDS matter much at all? What if I were to be using a chemical filtration media such as Purigen or Chemi Pure (does activated carbon count?)?

Chlorine 0.15-1.57 ppm MAX
Haloacetic Acids (HAAs) <1.0-39 ppb MAX
Nitrate 0.2-0.88 ppm (my tests always show 0ppm at the tap, yes calibrated, although the color chart isn't the most accurate indicator)
TTHMs (Total Trihalomethanes) 0.5-44.4 ppb
Radium 228 <1.0-1.29 pCi/L
Gross Beta Particles <3.0-7.98 pCi/L

Iron 0.047-0.109 ppm
Manganese 0.001-0.076 ppm

Fluoride 0.60-1.28 ppm
Turbidity 0.03-2.38 ntu

Total Coliform 0%

Sodium <5.0-16.0 ppm
Hardness 16-136 ppm

Copper 0.56 ppm
Lead 0.003 ppm


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## Argus (May 22, 2013)

WaterLife said:


> Thanks for the info Argus.
> 
> So the carbonates and bicarbonates are carbon sources and plants would use them up?


I believe so. 



> In the 55 gallon hillstream tank, there is no plants and no algae at all (tank light died a months ago, haven't replaced yet, they get by with varied algae wafers/gel and vegetables), literally just fish, so I'm not sure why the KH is really low for that tank, but it has been 3-4 weeks since a water change on that tank, maybe that has something to do with that, does it deplete any other way, evaporation? or???


I'm not really sure. I believe that acids will deplete KH. Bacteria that convert ammonia and nitrites to nitrates create acid. However, this should cause pH to drop.

Here is an interesting read on "old tank syndrome."


How are the other paramters of the water—ammonia, nitrites, nitrates? If you have a 



 (total dissolved solids) it might be interesting to see what it says. Meters can be had for less that $10.

Hopefully, Diana will chime in here. She seems to know a lot about this topic. I know just enough to be dangerous. 



> At least its good to hear it's easily increased.
> 
> But I don't get how the pH still remains at 7.4 with the KH being so low in some tanks. I was under the impression the pH and hardness levels are in similar relation to one another.


I don't understand that either. I thought pH had to do with the ratio of GH to KH, but I'm a bit fuzzy on this.



> That is why I am wondering if my silica sand (silicates) has anything to do with any of this. How different are silicates from phosphates/phosphorus?
> I will do all the tests again later today to double check values.


Silica sand is generally inert. Melt it and you get glass. That doesn't mean there couldn't be something else in the sand, but usually you find alkali buffers in sand, not acid.


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## Audionut (Apr 24, 2015)

For some strange reason, I can't quote your post Argus.



> I believe so.


Correct. Adding a carbon source (CO2) will reduce the rate of consumption of carbonates. I'm not entirely sure, but I believe plants revert to consuming carbonates due to a lack of easier carbon sources (CO2).



> I believe that acids will deplete KH. Bacteria that convert ammonia and nitrites to nitrates create acid. However, this should cause pH to drop.


Acids will deplete KH by adding H+ ions to the water. These H+ ions combine with Carbonate (







) to form Bicarbonate (







), and with Bicarbonate to form Carbonic acid (







).

Note in the chemical formula how the H+ ion is added to CO3 to form HCO3, and to HCO3 to form H2CO3. So bicarbonate contributes half to KH compared to carbonate, since bicarbonate already contains a H+ ion, and so can only accept one other H+ ion. Carbonate can accept 2 H+ ions to form carbonic acid.

My knowledge gets a little sketchy here, but while KH and pH can generally be considered somewhat mutual, it's probably best if we all stop making this general assumption. Consider a water source that contains carbonates. Adding a bunch of H+ ions won't initially create carbonic acic, since these H+ ions first combine with carbonate to form bicarbonate. So KH can be reduced by a factor of two, but the buffering capacity (Total Alkalinity) of the water remains high.

Carbonic acid is itself a weak acid. And if I understand correctly, doesn't maintain a high concentration in water since it forms CO2 (







). Reference Bjerrum plot. This CO2 then precipitates from the water through gas exchange.

So the carbon dioxide, hydrogen ions, bicarbonate and carbonate ions are at an equilibrium that maintains a pH of 7.4 (even though KH drops). The pH will drop when the equilibrium is significantly shifted to the left (in the Bjerrum plot). This probably won't occur until KH is almost non-existent.

My disclaimer is in my sig.


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## Diana (Jan 14, 2010)

GH is a measure of calcium and magnesium. These minerals are used by fish and plants, but not usually in enough quantity to notice on hobby level test kits. Not related to pH. 

KH is a measure of bicarbonates and carbonates. As explained by Audionut, this acts as a buffer to the pH. When acids are added (essentially increasing the H+) the bicarbonates and carbonates tend to stabilize the pH by removing the H+. 
Generally, but not all the time: 
If KH is high, the pH tends to be high, and not easily changed. (lots of bicarbonates and carbonates to keep on removing the H+). 
If the KH is low the pH tends to be low, and is more easily changed. 
There may be other buffers in the tank, though, other chemicals that also control the pH. Usually carbonates and bicarbonates are the big ones, but phosphates, sodium hydroxide, peat moss and other organic matter, and several other things can alter the pH. 
Roughly half the plants we keep in aquariums can use the carbon from carbonates when there is a lack of CO2 in the tank. 
Nitrifying bacteria get their carbon from inorganic sources like carbonates. 

GH and KH are measured in the same way. 
When using the API test kits, following the instructions, 1 drop of reagent = 1 German degree of hardness. No need to do any math, but if you want to, 1 German degree of hardness = 17.9 parts per million or milligrams per liter. When you post include whatever units you are using. 

6dGH is moderately soft, and plenty high enough to provide plants and fish with all the minerals they need. Most soft water fish are OK at this level. Hard water fish would prefer higher GH. 
7dKH is high enough to stabilize the pH. In the non-planted tank, I think the nitrifying bacteria are using it, especially if you have not done water changes recently. Look into the old tank syndrome. Low KH is certainly one symptom. 


Which pH test are you using? If you are using API high range test, this bottoms out at about 7.4. Varying shades of brown and purple, in the mid 7s it it yellow. It won't read any lower. 
You should also test with the API pH test that reads through the blues and greens. High end with this test is the mid 7s, and it goes down into the 6s.


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## Audionut (Apr 24, 2015)

Diana said:


> Usually carbonates and bicarbonates are the big ones, but phosphates, sodium hydroxide, peat moss and other organic matter, and several other things can alter the pH.


Small nitpick Diana. In terms of this conversation, I'm sure you meant, "several other things can _buffer_ the pH", even though they do alter the pH.




Diana said:


> Nitrifying bacteria get their carbon from inorganic sources like carbonates.


Indeed. And since they don't produce H+ ions, KH drops without pH changing. edit: Actually, I don't believe this is an accurate statement. More knowledge is required.


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