• You are viewing the forum as a Guest, please login (you can use your Facebook, Twitter, Google or Microsoft account to login) or register using this link: Log in or Sign Up

Water Reports - the Basics, as I am not getting the math!

Bradders

Bradders

Member
Joined
11 Dec 2023
Messages
808
Location
United Kingdom
Hi All,

I have read on the internet and read some threads here, but I am finding it hard to settle on an understanding of how to use a water report to understand (roughly) the out-of-the-tap GH and KH. I am going around in circles!

Would someone very kindly look at this water report (attached) from my local area and let me know what parts are needed to understand the GH and KH? I know I can measure my tap water (and have) but for the life of me I cannot work out how the numbers I get back are calculated using the data within the report.

I really would appreciate a basic master class to get me started. Sorry that this is something that has been asked time and time again - I am just not getting it!

Thanks,
Brad
 

Attachments

  • Z609.pdf
    319.4 KB · Views: 38
Is it this?

Screenshot 2024-03-27 at 13.21.09.png
 
Hi @simon_the_plant_nerd - thanks, but I may have misled you!! (Sorry!)

The above attachment is my work based on what I got from the Water Report I attached to the original post. The actual water report says my water is Moderately Hard to Hard. (See screenshot below from the report).

I was trying to work out a) the GH and b) the KH based on the information in the Water Report. i .e.
  1. KH - CaC03 for the KH, which I think is CaC03 / 17.8 to get dKH.
  2. GH - Calcium and magnesium for the GH, which I think is a different math:
    1. 7.1ppm of Calcium = 1 dGH
    2. 4.3ppm of Magnesium = 1dGH
So the question is, have I actually got my head around this or am I still miles of?!? :D
Screenshot 2024-03-27 at 14.47.48.png
 
Bradders said:
Hi @simon_the_plant_nerd - thanks, but I may have misled you!! (Sorry!)

The above attachment is my work based on what I got from the Water Report I attached to the original post. The actual water report says my water is Moderately Hard to Hard. (See screenshot below from the report).

I was trying to work out a) the GH and b) the KH based on the information in the Water Report. i .e.
  1. KH - CaC03 for the KH, which I think is CaC03 / 17.8 to get dKH.
  2. GH- Calcium and magnesium for the GH, which I think is a different math:
    1. 7.1ppm of Calcium = 1 dGH
    2. 4.3ppm of Magnesium = 1dGH
So the question is, have I actually got my head around this or am I still miles of?!? :D
View attachment 217527
Click to expand...
Yes, you did mislead me. But now I’m doubting what I thought I knew as I’ve just discovered that dGH is 10mg/l CaO of 17.8mg/l of CaCO3 so does that mean dGH takes into account KH too? I will wait for someone smarter to come along and explain. 😄
 

Attachments

  • IMG_6444.jpeg
    IMG_6444.jpeg
    243.9 KB · Views: 12
Indeed. This is what I read. Does this help - and is it even right?
17.8ppm of Calcium carbonate (CaC03) dissolved in 1 litre of water only gives 7.1ppm of Calcium (and therefore 10.7ppm of Carbonates). Having 7.1ppm of Calcium in your water is equivalent to having 1dGH.
Click to expand...
Math:
  • 1 dGH = 7.1ppm of Calcium
  • 1 dGH = 4.3ppm of Magnesium
  • Add both Calcium and Magnesium together to get GH/dGH.
 
Bradders said:
I was trying to work out a) the GH and b) the KH based on the information in the Water Report.
Click to expand...
You have around 13 dGh from 80ppm Calcium and 8.5ppm Magnesium.

dkh is also sitting around 13 dkh from 234ppm CaC03.

So fairly hard water.

Edit: as above, darrel will explain it far better than I can.
 
Hi all,
simon_the_plant_nerd said:
knew as I’ve just discovered that dGH is 10mg/l CaO of 17.8mg/l of CaCO3 so does that mean dGH takes into account KH too? I will wait for someone smarter to come along and explain.
Click to expand...
"Yes and no" is the answer, they are separate entities, but you can define both "1 dGH" and "1 dKH" as 17.86 mg / L of CaCO3. <"The calculations"> are all in Larry Frank's very useful post on the Krib <"Water Hardness">.
1dKH = 17.86 ppm CaCO3
From above; 1dKH = 17.8575 mg/liter CaCO3. 7.143 mg/liter of this is Ca, the rest ;(17.8575-7.143)= 10.7145mg/liter CO3
1dKH = 10.7145 ppm CO3
Click to expand...
cheers Darrel
 
simon_the_plant_nerd said:
so does that mean dGH takes into account KH too?
Click to expand...

Yes, sometimes it does... If we have say 30 ppm of Ca from CaCO3 you get 45 ppm of CO3.

This translates into 4.2 dGH and 4.2 dKH. Notice that CaCO3 contributes equally to dGH and dKH (which seems to be confusing for many at first).

Often in the hobby we have dGH and dKH decoupled, but we can reach the same dGH and dKH by other means than CaCO3 (adding CaCO3 to increase KH significantly is not practical given its almost insoluble):

So for instance if we have 30 ppm of Ca from CaSO4 we get 4.2 dGH and zero contribution to dKH.

Likewise, if we have 45 ppm of CO3 from K2CO3 we get 4.2 dKH and zero contribution to dGH.

Additionally, if we would have 30 ppm of Ca from CaCO3 and add 30 ppm of Ca from CaSO4 we will get 60 ppm of Ca which translates into 8.4 dGH... but we still maintain the 4.2 dKH as we didn't change the amount (45 ppm) of CO3.

EDITED: for clarity - hopefully :)

Cheers,
Michael
 
Last edited:
simon_the_plant_nerd said:
The unit of degrees hardness most used in aquarium test kits (and fish keeping literature as far as I can see) are equal to 17.8mg/l.
Click to expand...
Just to try to explain this confusion and hopefully not confuse people even more, many tests use the unit "ppm of CaCO3 equivalent" for calcium concentration. The test measures the concentration of calcium ions and then they do this math juggling where they say how much would the calcium weight it it was CaCO3, or in other words, how much CaCO3 you would need to add to pure water to reach the measured concentration of Ca. Clearly, the molecular weight of CaCO3 is higher than only Ca, so the concentration given in ppm of CaCO3 equivalent is a larger number than the concentration given simply as calcium. And when you convert this larger number into dGH, you divide by a large number (17 and some decimals). But if you have the small number of real calcium concentration in ppm, you have to divide by a smaller number (7 point something).
 
Last edited:
So, in short, are we saying the above comments match up with the below (from the internet)?
17.8ppm of Calcium carbonate dissolved in 1 litre of water (which is 1dGH) actually only gives 7.1ppm of Calcium (and 10.7ppm of Carbonates). Having 7.1ppm of Calcium in your water is equivalent to having 1dGH. Hobbyists often make the mistake of converting dGH to ppm in terms of Calcium by just multiplying the dGH value by 17.8 which is wrong, as this includes the mass of the Carbonate (CO3) anion.

In short:

1 dGH = 7.1ppm of Calcium = 0.178 mmol/L of Calcium ions

1 dGH = 4.3ppm of Magnesium = 0.178 mmol/L of Magnesium ions

If you have for example, 14.2ppm of Calcium and 4.3ppm of Magnesium in your tap water, then you have exactly 3 dGH (2 dGH of Calcium + 1 dGH of Magnesium). In another example, if you have zero Calcium in your water, and 43ppm of Magnesium, you would still have water that measures 10 dGH. The dGH measurement/reading does not discriminate between Calcium and Magnesium (or other divalent ions). Calcium and Magnesium are both required by plants while some livestock such as shrimps care for Calcium but not Magnesium. Thus using the dGH measurement is really an imprecise tool for managing tank parameters compared to directly measuring Calcium and Magnesium levels.
Click to expand...
 
Right, thank you MJ and all. I think I am beginning to understand!
 
MichaelJ said:
This translates into 4.2 dGH and 4.2 dKH. Notice that CaCO3 contributes equally to dGH and dKH (which seems to be confusing for many at first).
Click to expand...
I understood the rest of your message but can I just clarify this bit for my tired brain:

The Ca in the CaCO3 contributes 7mg/l (approx) and the CO3 contributes 10mg/l approx.

Approx 7mg/l of calcium is 1dGH
Approx 10mg/l of CO3 is 1dKH

The 17.8mg/l comes from the combined mg/l of dissolved ions. The assumption is made that all ions contributing to hardness is from CaCO3.

The 17.8mg/l is no longer useful once the ions contributing to general hardness and carbonate hardness are decoupled?

So when I mix up my calcium chloride with deionised water to make a solution of say 10dGH I’m adding ~70mg/l of calcium. The chloride contribute to neither dGH or dKH so I have a 10dGH and 0dKH solution?
 
simon_the_plant_nerd said:
So when I mix up my calcium chloride with deionised water to make a solution of say 10dGH I’m adding ~70mg/l of calcium. The chloride contribute to neither dGH or dKH so I have a 10dGH and 0dKH solution?
Click to expand...

That is correct. General Water Hardness (dGH) is defined by the contents of Calcium, Magnesium and technically certain trace metals like Iron and Manganese (we usually wont concern ourselves with those because their impact are minuscule) nothing else. The original concept really came out of a need to be able to quantify a water source potential detrimental effect on piping, valves etc. at the early stages of the Industrial Revolution as hard water will leave a scale deposit (lime scale) that will eventually clog up pipes, valves and boilers etc. - a big issue in steam engines back in the day - see Thomas Clark.

Chloride, Sulphates and Potassium - minerals we often add in abundance, wont impact our water hardness by definition, but it will certainly impact our Electrical Conductivity (EC/TDS) which directly impact our livestocks osmoregulation. So we can have soft water (low contents of Calcium and Magnesium), but still have a less than ideal environment for our soft water species, say if we have a lot of Chlorides, Sulphates, Potassium and other minerals that wont count towards our General Hardness. As you can tell, dGH is only partially valid to assess the appropriateness of our aquarium water.

The only thing that counts towards dKH (Carbonate hardness or alkalinity really...) is the CO3 contents - technically the bicarbonate (HCO3-) and carbonate (CO3-) anions.

Cheers,
Michael
 
Last edited:
You must log in or register to reply here.
Back
Top