Interpreting Tap Water Analysis GH=6, KH= 7 or 9.5

J

Jhereg10

AC Members
Jun 1, 2003
32
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0
Houston, TX
www.dscworld.org
My water department was nice (and fast) and faxed over an analysis of my tapwater supply today.

My testing gave me pH=7.5, GH=6, and KH=6 for my tap water last week.

Unfortunately, the analysis isn't completely straightforward.

I have one page titled "Metals".

It lists (all in mg/l)

Aluminum <.05
Arsenic 0.003
Barium 0.32
Cadmium <0.001
Calcium 34.3
Chromium <0.01
Copper <0.006
Iron 0.24
Lead <0.001
Magnesium 5.0
Manganese 0.02
Mercury <0.0004
Nickel <0.02
Selenium <0.003
Silver <0.01
Sodium 36.5
Antimony <0.004
Beryllium <0.001
Thallium <0.001
Zinc <0.02
Total Hardness as CaCO3 106

I'm pretty sure the total hardness listed here is actually GH.

This seems to make sense, because if you add the Ca (34.3) and Mg (5.0) and do that complex calculation to convert to equivalent CaCO3, you get 106 mg/l. Which would be a General Hardness of 6 dGH.

Now the next page is titled "Minerals" in mg/l

Chloride 30
Flouride 0.7
Nitrate <0.01
Sulfate 9
pH 7.3
Dil. Conduct (umhos/cm) 396
Total Alka. as CaCO3 134
Bicarbonate 163
Carbonate 0
Dissolved solids 196
P. Alkalinity as CaCO3 0

Ok, now pH is listed clearly, and is within range of what I measured (7.3 vs. 7.5). I figure some variablility is to be expected.

And KH is based on the listing for Bicarbonate and Carbonate only, right? And that would be 163 mg/l which equals about 9.1 KH. But what is this thing they are calling "Total Alka." (134=7dKH) and "P. Alkalinity" (0!!!). Hmm...

So I seem to have a GH of 6 and a KH of either 9.1 or 7, depending on whether I just use Carbonates and Bicarbonates or I use the heading they listed as "Total Alka."

I'm a little confused, because I understood that:

General Hardness (GH) = Permanent Hardness + Carbonate Hardness (KH)

And based on above I get a GH that is LESS than my KH, meaning I would have a negative Permanent Hardness...which seems really counterintuitive.

Any thoughts on this? Side note, I found out my water system uses chlorine, not chloramine.

Also, anything else on the analysis look like something I should watch out for? Oh, the other funny thing is that my LFS who seemed to know what he was talking about claimed our water was "quite hard" but my understanding is that 6dH for GH is actually categorized as "soft". Even 9dH for KH would be on the lower edge of "medium hard". We're on the same water system, does this mean my LFS isn't as knowledgeable as I might think?

Thanks!
 
GH is a measure of the calcium and magnesium as you state, but GH testing is expressed as ppm or degrees of CaCO3. In other words, the test is read as if it were distilled water containing the reading amount of CaCO3, fulll dissolved. Therefore the GH = 6 degrees (you cannot properly specify a number unless you also specify what the units are - in this case degrees or ppm). GH = 6 degrees or ~107ppm CaCO3. (one degree = 17.86 ppm)

KH tests measure alkalinity, expressed as if the same standard material had been read, CaCO3. The alkalinity, or carbonate hardness, is in reality a measure of the buffering capacity of the water and can be influenced by other materials. An actual analysis of the carbonates will only measure the same as the measured KH if it is the same hypothetical CaCO3 in DI as mentioned before. You cannot directly convert to KH from analysis of the carbonate and bicarbonate ions unless there are no other materials in the water which would effect the buffering capacity. That is all but never the case in real-world water.

Don't get yourself twisted up with permanent and temporary hardness. Stick with cacium hardness (really Ca & Mg hardness) which can affect egg membranes and breeding of soft or black-water fish, and with KH, carbonate hardness (in reality buffering or alkalinity) which reflects pH and its stabilty.
 
Um...ok, I THINK I understand your response.

The GH I can use directly, because it is only Ca and Mg, and I have hard numbers for those. It is, as I guessed, 106 mg/L or about 6 dH.

The KH I can't just take the Bicarbonate reading from the analysis, because KH is a measure of the TOTAL buffering capacity (which while bicarbonate and carbonate are the greatest factors, there are others) measured in an equivalent amount of CaCO3 in DI water.

So from their analysis, it's more likely the value titled "Total Alka. as CaCO3" with a value of 134 mg/l is the actual total buffering capacity. This would give a KH of about 7dH.

Last question, is it then possible to have a KH greater than GH?

Thanks much!
 
Wow! Now I get it. Thank you very much, that was a most enlightening article.

The highlights of the author's argument:

Rule #1: It is far more important to have a stable system (pH, KH, GH, TDS) than to attempt to duplicate a particular fish's native environment. Thus, you should just use your tapwater "as is" (dechlorinating of course) and not try to tinker with it if at all possible. This is the case for most community aquariums or where breeding is not the focus. Correct?

This is exactly what my LFS tried to tell me, and I thought he was nuts at the time....argh.

Exceptions to Rule #1: Tap water that is completely unacceptable, in which case you may have to tinker with it or use RO or DI water. Situations where successful breeding requires very specific conditions for that fish species. Situations where the fish are extremely delicate.

Rule #2: For the large majority of hobbyists (ergo, for most fish) the following is acceptable tapwater not needing adjustment:

pH 6.5 to 7.5 (For many community tanks, 6.0 to 8.0)
GH 3-5 min. to 12-18 max
KH 3-5 min. to 10 max

Exceptions to Rule #2: HOWEVER, if your species requires VERY hard or soft (Discus, Apistogramma, some Blackwater tetras, Rift Lake, and some Central American fish), or acid or alkaline water, you may have to resort to "doctoring" the water.

But the big thing is STABILITY regardless of where the pH, KH, and GH are set.

So, all those pH increasers, decreasers, buffers, etc, are in large part marketing driven, and not need-driven for most hobbyists?

Correct?
 
It is really because most hobbyists do not in truth study their fish or their needs - they hear or read that Tetras like soft acid water and don't know better than to think that adding more things to the tank water will make it "softer", rather than the reality that it does the opposite and increases the TDS. Then they roller-coaster the pH with so-called buffers and stress the fish.

If you are breeding fish from the extremes and which are not multi-generation tank bred, you need to do water mods, correct. If you are maintaining fish, stability is what is most important. It is also what is easiest and cheapest to provide.

BTW, I am the author. It is just easier to ref. already published material than write every anew.
 
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