# Hardness vs Alkalinity



## harif87 (Jun 5, 2006)

I was reading up on the water quality report for my area on the water quality of 2005 and i noticed that they had 2 terms which seemed to be synonomous but were listed with 2 different values. They had alkalinity (mg/L CaCO3) at 13.5 and another term Hardness (mg/L CaCO3) at 20. I always thought that alkalinity (besides for its reference to pH) was the same thing as water hardness. Furthermore they used the same units for both Hardness and Alkalinity. Anyone have any insight on this?

Another question, is silica the same as silicate? If not, is it just another form which can turn into silicate?


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## BIT01 (Jun 18, 2006)

For the first part alkalanity is the willingness of a substance to recieve H+ ions (protons) or how basic the substance is. Hardness is the hydronium(H3O+)-hydroxide(HO-) concentrations of the water. since water is not a normal compound it will occasionally give a H to another water molecule. 

The terms are related in the fast that they deal with the ionization of the water but are not synnonmous

The next part is they aren't synonomous

silica is silicone dixide(SiO2) a silicate is anything that contains one or more silicon as an anion(+) so silica is a silicate. 

sorry I couldn't do the subscripts


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## harif87 (Jun 5, 2006)

BIT01 said:


> For the first part alkalanity is the willingness of a substance to recieve H+ ions (protons) or how basic the substance is. Hardness is the hydronium(H3O+)-hydroxide(HO-) concentrations of the water. since water is not a normal compound it will occasionally give a H to another water molecule.
> 
> The terms are related in the fast that they deal with the ionization of the water but are not synnonmous


Which is why both water hardness and pH can both be referred to as the alkalinity since a Base is an alkaline (it accpets a proton) and CaCO3 which is also a base that buffers the water from pH change by accepting the loose H+ protons.

Also when you said "Hardness is the hydronium(H3O+)-hydroxide(HO-) concentrations of the water." i am assuming you meant pH since thats the exact definition of pH. 

Here is the site if you want to take a look at what im talking about : http://www.ci.nyc.ny.us/html/dep/pdf/wsstat05.pdf
Its on page 12 with all the other statistics


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## BIT01 (Jun 18, 2006)

no it has no effect on ph cause there is always the same amount of both HO- and H3O+ at any given time. They cancel each other out. It's the amount that they appear in a ratio with the H2O.


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## harif87 (Jun 5, 2006)

BIT01 said:


> no it has no effect on ph cause there is always the same amount of both HO- and H3O+ at any given time. They cancel each other out. It's the amount that they appear in a ratio with the H2O.


What has no effect on pH?


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## BIT01 (Jun 18, 2006)

the H3O+ HO- concentration. They cancel each other out because the H+ ions never leave the water. a balanced eq would look loke this 2 H2O <--> H3O+ + HO- I know that is hard to read but that's cause of formatting issues.


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## harif87 (Jun 5, 2006)

I think your missing the point, sorry


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## Damon (Jan 18, 2005)

I think you're making this a little too complicated............

kH
Carbonate hardness or temporary hardness. Measures the buffering capacity or the ability to absorb and neutralize added acid without major changes to pH. Think of buffering capacity as a big sponge, the higher the buffering, the bigger the sponge. How much buffering does your tank need? The higher the kH (the bigger the sponge), the more resistant to pH changes your water will be. A tank's kH should be high enough to prevent large pH swings over time. If your kH is below roughly 4.5 OdH, you should pay special attention to your tank's pH (e.g., testing periodically) until you get a feel for how stable the pH is.
Buffering is both good and bad. On the good side, the nitrogen cycle in our tanks produces nitric acid (nitrate). If we don’t have buffering (kH), the pH will drop over time. Sufficient buffering will keep the Ph stable. On the bad side, hard water almost always has a large buffering capacity and if the pH is to high for your fish, this large buffering capacity will make it more difficult to lower the pH.
Buffering is sometimes referred to as "alkalinity" but should not be confused with "alkaline". Alkalinity refers to buffering and alkaline refers to a solution that is base rather than acid (pH).

gH
General hardness (GH) refers to the dissolved concentration primarily of magnesium and calcium ions. Other ions can contribute to water hardness but are usually insignificant and difficult to measure. When fish are said to prefer ``soft'' or ``hard'' water, it is gH, not kH that is being referred to. gH will not directly affect pH although "hard" water is generally alkaline due to some interaction of gH and kH.
Incorrect gH will affect the transfer of nutrients and waste products through cell membranes and can affect egg fertility, proper functioning of internal organs such as kidneys and growth. Within reason, most fish and plants can successfully adapt to local gH conditions, although breeding may be impaired.
Most test kits measure gH or general hardness in German degrees hardness or OdH, which is equal to 17.9 mg/L. Since mg/L is equal to ppm (parts per million) simply multiply the degrees OdH times 17.9 if you prefer to work with ppm. The following table will give an idea of how hard your water may be after reading the test results.

In shrot kh is temporary, gh is permanent. You can drive of carbonate ions to reduce kh. You have to filter out gh (as in ro unit).


Info taken from http://www.drhelm.com/aquarium/chemistry.html


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## harif87 (Jun 5, 2006)

Maybe i did make this too complicated lol

Im well aware of what the terms GH & KH (and pH) mean.

Here is the question paraphrased; why does the report show values for Hardness and Alkalinity? In the report it measures the alkalinity(mg/L CaCO3) and the carbonate hardness (mg/L CaCO3) - which is the same thing. It measures the general hardness with other values (Ca2+ & Mg2+ in mg/L) and thats not what the other "hardness" value i am refering to.

If im being too complicated just ignore the Q.


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## Damon (Jan 18, 2005)

Never too complicated. Alkalinity and hardness are synonymous in most uses.......

But they are not the same thing................
There are other elements (ions if you will) that can contribute to alkalinity but not carbonate hardness (non-bicarb alkilinity). It is rare in the U.S. but not unheard of and more common in other parts of the country. 


KH deals with strictly carbonate and bicarb hardness
Gh deals with calcium and Magnesium hardness
Alkalinity deals with kh AND all other non carbonate alkaline ions
Total hardness is the sum of alkalinity and gh


http://www.thekrib.com/Plants/CO2/hard-slu.html


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