5 replies to this topic

[Cicolid]

How to convert your kH/gH reading from ppm to degrees (or degrees to ppm)?

KH or GH readings in parts per million (ppm) can be converted to degrees by dividing them by 17.86. For example, if your KH tests as 120 ppm, this means your KH is 6.7 degrees.

To convert gH/kH to ppm just multiply by 17.86.

[sydad]

I guess that this doesn't rate as an "FAQ", but it's one I've asked before, so I'll ask again:

Why would anyone bother to convert to "degrees" of hardness (GH or GDH) that is the outdated, nonsensical German system, often called DIN (Deutsche Industrie Norm).
As far as I can see, it was a system set up by the Germans to confuse the rest of the world as thoroughly as the equally stupid British (Clark and Lubbs) system for rating the same. At least the Poms recognised the futility of their system, and consigned it to history books, but because so much otherwise useful aquarium literature has originated in Germany, those good folk think it's acceptable to everyone else to live in the past.

Let's move on and use the more logical ppm ( mg/l), or better still molar concentration. This latter actually tells us about relative "activity" of dissolved substances, and makes infinitely more sense, though it does necessitate learning a little about molecular weights.

Those wishing to nail my hide to a tree for committing what they see as sacrilege, are welcome to do so, but please try a logical defence other than "it's been done this way forever, so it must be OK"

Syd.

[Cicolid]

Hi Syd,

I posted the FAQ because I thought it would help some members.

Very good point & I agree it would be far easier for everyone if we only had the one measurement.

Some of the most popular test kits use measurements of degrees gH/Kh and others use ppm. You have now thrown another measurement (mg/L) into the equation.

If you wish to comment/complain or change the measurement system can I suggest that you contact the manufacturers of the test kits, because until they all use a uniform measurement system the above FAQ with be relevant.

These test kits are made in several different countries, and cannot even agree on a uniform measurement as basic as feet & inches v's metres how do you expect them to agree on this.

Cheers
Col

[sydad]

Hi Col,

I fully understand your reason for posting the information, and I am in no way criticising you. I was trying to make the point that we as aquarists tend to accept things uncritically and without thought. I have tried suggesting to test-kit manufacturers that the "degree of hardness" nonsense should be discontinued, but get short shrift as they "feel that these units simplify matters for aquarists". Makes one wonder how they would go about making those matters more complex!
The way to look at this is to buy only those kits that emphasise the more logical units of measurement.
At best it's going to be a long uphill battle before we see sense, but I console myself with the knowledge that "mighty oaks from little acorns grow", so I'll persist in hitting my head against the brick-wall of tradition and hope for the best.

By the way; ppm and mg/l are identical figures in aqueous systems: that is , they are just different ways of saying the same thing, with mg/l being the more logical expression.

Cheers,
Syd.

[Cicolid]

By the way; ppm and mg/l are identical figures in aqueous systems: that is , they are just different ways of saying the same thing, with mg/l being the more logical expression.
Cheers,
Syd.

Hi Syd,

Thanks very much for that, I didn't realise that ppm & ml/L are the same. You have saved me a lot of time researching the subject.


BTW. Don't you find it amazing that the USA is supposed to be the most up-to-date modern country in the modern world, yet they still use Pounds & ounces, & feet & inches, and what is more they expect us to do the same.

Col

[keenas]

Si units have not been adopted world wide. In my industry we have issues with Australian standards, various state standards. UKAS(UK standards) and ASTM(American standards). Along with other governing bodies, they all state essentially the same thing, however they also seem to want to stamp their authority on each standard. I guess thats the world we live in isnt it.