New Hardness (CaCO3) test kits

[tjudy]

Hi All...

I have gotten some chemical reagent test kits for water hardness from Hanna Instruments, and my first impression of them is very good. They are low range kits (0-150ppm) rated for 100 tests. They have a large test bottle that will not get over full like the small cuvettes of some other test kits, and they are easy to swirl. The dropper bottle is easy to control, and I have not experienced any 'over-dripping'. I tested them on several different water sources, and they seem pretty accurate. My R/O-DI water READS zero..WOO HOO!.... I used that and tap to create varied concentrations. I will set up a more rigid test later this week... I have some students who need the extra credit.

The precision is 5ppm CaCO3.

Does anyone know the ppm to KH or degrees hardness conversion off the top of their head?

The test kist are also CHEAP... we will sell them in the store for $7.00.

 

[farm41]

Is there any reason to use one of these if you have a nice EC meter?

 

[hedylogus]

This is a cut & paste from a document I saved a while back:

By definition, 1 dGH = 10 ppm CaO. Or, 1 German degrees general hardness is obtained by dissolving 10 milligrams of calcium oxide into 1 liter of water. Or, 1 dGH equals 7.1 ppm Ca++ (calcium ion). Or, 1 dGH equals 17.9 ppm CaCO3 (calcium carbonate). The last conversion is sometimes stated as ppm Ca++ as CaCO3.

By definition, 1 dKH = 10.7 ppm CO3--. This one is not straight forward, because the carbonate ion CO3-- only exists while dissolved in water (and other solvents). So immediately you need conversion factors. Dissolving 17.9 mg CaCO3 in to 1 liter of water will raise the dKH by 1 degree. Or, 1 dKH = 21.8 ppm HCO3-.

Hope that helps.

 

[tjudy]

Thanks hedylogus..

Matt... an EC meter measures TDS (dissolved solids). Carbonate hardness is a different measurement. Carbonate denote buffering capacity, and make the water alkaline. It is possible to have a high pH due to carbonates, but low EC (dissolved solids). No meter can measure carbonate hardness. THere are some spectrophotometers that measure color change very accuraltely, but they still require the use of reagent chemicals.

 

[farm41]

So, can I assume that a low PH means a low carbonate hardness?

 

[tjudy]

Usually a low pH is indicative of a low hardness, unless there is a LOT of acid being produced. CaCO3 'absorbs' acidity.. but if the acidity is being produced rapidly the buffering capacity of the carbonates can be overcome. If you are using the RO you likely have pretty low carbonates.