# Hardness, making 4 dkh water



## mcsinny99 (Sep 2, 2008)

My local water treatment facility updates parameters on a weekly basis and current tap water parameters for hardness are 8.07. My question is if I add 50% distilled water to tap will that leave me with a 4dkh solution for a co2 drop checker?

Hardness mg/L (gr/gal) 10/23/2008 138 (8.07)


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## jmontee (Feb 7, 2008)

The main problem with that is that there are other things in the tap water that may contribute to the buffering of the solution.

The other question is if they are talking about alkalinity or general hardness. kH is the carbonate hardness which is what you are looking for but most water treatment parameters are for GH which is the measure of dissolved solids. This includes calcium and other ions that cause staining of pipes and such. Make sure that they are saying it is kH and not GH that is 8.07. You should also make sure of the units they are using. Is it ppm or degress etc.

There are several recipes for making 4dkH water here or pm me if your interested in purchasing some (really cheap just need to cover costs.)

Edit: Sorry I didn't notice the results you posted. That looks like it is about the General Hardness and not kH.


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## ray-the-pilot (May 14, 2008)

No! your water Co. seems to be talking about general hardness. If you dilute this 1/2 you will have no idea what the kH is. 

To make 4 kH water for your drop checker, dissolve 1.2 gm of baking soda (NaHCO3) in one liter of distilled water. Then take 100 ml and dilute it to 1 liter with distilled water. This solution is now 4 kH.


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## Squawkbert (Jan 3, 2007)

ray-the-pilot said:


> No! your water Co. seems to be talking about general hardness. If you dilute this 1/2 you will have no idea what the kH is.
> 
> To make 4 kH water for your drop checker, dissolve 1.2 gm of baking soda (NaHCO3) in one liter of distilled water. Then take 100 ml and dilute it to 1 liter with distilled water. This solution is now 4 kH.


Give or take ~10%. Baking soda tends to have a fair amount of moisture with it. Unless you know how much moisture is there, you can't adjust your weight accordingly. Oven drying it is no good as you'll start converting it from bicarb to carb before you drive all of the water off. If you don;t have a Karl Fischer titrator, just buy some standard 4dKH solution. There are a few vendors who sell 500mL bottles of it for not a lot of $ (500mL - enough for a club purchase!).


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## ray-the-pilot (May 14, 2008)

Squawkbert said:


> Give or take ~10%. Baking soda tends to have a fair amount of moisture with it. Unless you know how much moisture is there, you can't adjust your weight accordingly. Oven drying it is no good as you'll start converting it from bicarb to carb before you drive all of the water off. If you don;t have a Karl Fischer titrator, just buy some standard 4dKH solution. There are a few vendors who sell 500mL bottles of it for not a lot of $ (500mL - enough for a club purchase!).


While that is true, it is not significant. 
Concentration is a linear scale while pH is logarithmic. What that means is at a concentration of CO2 = 30 ppm the pH of a 3.6 kH solution is 6.56. The pH of a 4.0 kH solution is 6.60 and the ph of a 4.4 kH solution is 6.64. You could not distinguish this variation in color by eye.

If you don't believe me go here and check it out yourself on the calculator:

http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

Unfortunately, even if use certified 4.0 water your results are at best only a rough estimate of the CO2 level.


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## Squawkbert (Jan 3, 2007)

^ good point (that I had failed to consider).

I looked at the calculator - and we're talking about a 10ppm swing in CO2 reading for an entire 1dKH swing around pH 6.5 (at pH 6.5, you get ~43PPM CO2 in a 4.5dKH, 33PPM CO2 in a 3.5dKH solution), so beyond a certain point, you're "close enough". Some people just like knowing that they're looking at a green checker and knowing that they're centered in the window ±1PPM vs. ±10PPM.


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