# How to use tetra GH test



## dukydaf (Aug 31, 2004)

I recentely bought Tetra GH test and i tested my water following the instructions.
They say that the color in the test vial turns from red to green.Thats ok so far but when to read it they say: "if the color cahnge occurs right after the first drop, the level is between 0-1*dh the number of drops added until color changes represents the level of hardness (German hardness).For instance, 3drops=3*dh"

My water colored from the first drop but with a slight red and after 2 more drops it was a white red so how can you figure out how many drops are enought. The color of the water changed from the first drop but i doubt that i have the GH=1*dh because my tap water is from the Danube (East Europe) so i expect a hard water.


P.S. I had a trip to the mountains in the other part of the country and the water from an almost pure spring was 3dh and was colored green???


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## HeyPK (Jan 23, 2004)

There is a problem with the Tetra GH test. As time passes, the color change gets harder to detect. With fresh chemicals, the change from red to green is quite pronounced, but with time, the red color becomes less and less. Instead you get a yellow color that becomes a little greener when you reach the change point of the test. If you have had your kit for three or more years, the change is very difficult to detect. Eventually, there is no change. You start with greenish yellow and it stays that way. Maybe your kit was on the shelf for several years before you bought it. They really ought to put an expiration date on those kits.

IF you got a rose or orange color initially, you should still be able to detect the change. Just keep adding drops until you see a color shift towards more green.


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## koffee (Aug 21, 2005)

dukydaf said:


> They say that the color in the test vial turns from red to green.Thats ok so far but when to read it they say: "if the color cahnge occurs right after the first drop,


I'm not familiar with this specific test kit. But from what you stated, it sounds like you are looking for the change to green.

So, when they say "change after the first drop", they probably mean green and not red. You are going to see a color change of the test sample when you start adding drops... for water that will register some GH above 1, you should see a change to red right away and then, after X number of drops, a change to green.

My alkalinity (KH) test kit works that way. By the way, doesn't "german hardness" usually refer to KH and not GH? (GH stands for General Hardness, I believe.)


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## titan97 (Feb 14, 2005)

German Hardness is a unit of measurement, like miles, kilometers, gallons, liters, etc. 

GH or general hardness is a way of defining the amount of calicum and magnesium are present in the water. It can be expressed in ppm, mg/L, german hardness, etc.

KH (aka alkalinity or carbonate hardness) is a measure of the total alkalinity in water. This is usually based upon the carbonate/bicarbonate/carbon dioxide equilibrium. It, too, is measured in ppm, mg/L, german hardness, etc.

-Dustin


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## koffee (Aug 21, 2005)

I never measured GH so I wasn't sure about it. I think I understand my confusion now. As far as I know, "german degrees" is a unit of measurement, and not "german hardness".

Maybe that is a shorthand way of saying german degrees of hardness but that would just add to the confusion (for me, at least) since, as I've now learned, you can measure both GH and KH using german degrees.


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## dukydaf (Aug 31, 2004)

*There has been a misunderstanding*

Sorry for my english because you understand that the color changes from red to green. That is not true they say that the color can be either red or green.

In fact the solution in the test bottle is green-blue.

I can not have a GH under 6 because after 1 day of DIY 5l bottle over my 62.5g the ph was down only 0.5 degres


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## Left C (Jun 14, 2005)

dukydaf said:


> Sorry for my english because you understand that the color changes from red to green. That is not true they say that the color can be either red or green.
> 
> In fact the solution in the test bottle is sowhat green-blue.
> 
> I can not have a GH under 6 because after 1 day of DIY 5l bottle over my 62.5g the ph was down only 0.5 degres


Your English is just fine. Many people get confused while doing these titration tests that involve a color change. I don't have the Tetra GH test kit so work with me a little. I have Hagen's and AP's kits.

You say the color of the solution is green-blue. This will also be your "finish" color also.
Let's say that you add one drop to your test tube and the color turns a red color. You add another drop and it is still a red color. You add another drop and it changes to a green-blue. This is your "finish" color. This means that the GH is 3. (When I use the Hagen, there's a little formula used: take the drops used times 20 to get ppm and multiply this number by 0.056 to get degrees. I'll get back to this in a minute. I believe your Tetra kit is not like this.)
Let's do another example, OK?
Let's say that you add one drop to your test and the color is green-blue. This is your "finish" color. This means that your GH is 1 or less.
Understand?
What you are looking for is:
1) a color change from whatever the color is in the test solution to a new color
2) add and count the drops until this new color changes back to the color it was in the solution (do not worry if it is not exactly the same shade of the color as shown, you are looking for a change) 
3) if there is no color change, (i.e. like the last example) then the GH is between 0 and 1

To convert between German Degrees and ppm is easy.
Take German Degrees times 17.86 equals ppm or,
Take ppm times 0.056 equals German Degrees

Have you got it now? 
(The main thing to look for are color changes and not necessarily matching the exact shade shown. Why, you ask? Your test water may be a little discolored from whatever water was used to set up the color standard. The little bit of contaminates in your water caused this discoloration.)


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## dukydaf (Aug 31, 2004)

*That idea does not work*

I tried your sugestion and added 17 drops of slution if you follow their instructions it gives you GH=17dh*. I grow neon tetra in that water so it can not be.

After about 10 drops the waer did not colored more in red so i figgure that my aquarium water has 10dh*

The solution was re d through out the test. From the first drop it had a small color of red and the it got reder until 10 drops. After this the coor change of the water was minimal.

Do you think im right?
Any other sugestion?


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## HeyPK (Jan 23, 2004)

If your solution turned red and got redder as you added drops, that means that the chemicals are fresh and the test is working properly. If the chemicals had aged and degraded, you would not get any red color at all, only a brownish green from the start. To me, it looks like you should have kept adding drops until the color turned from red to green. It seems likely that the hardness of your water is more than 17 DH, and this is quite possible. Keep adding drops until the solution turns green!!


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