dkh vs alkalinity

[nrbelk]

I think that is what I read and why I got confused and worried in the first place. If other chemical species could make a solution more alkaline (more basic?) then why could we take an alkalinity reading (which I think relates to base vs acidic) and have it mean the same thing as dkh (which I thought was a measurement of carbonates). I'm guessing my error was thinking that dkh was a measurement of carbonates... Or am I messing up again?

With what has been explained now I feel assured that I can use my hanna checker without worry

 

[nrbelk]

This is the paragraph from the article that Allmost linked to that I was missing in my brain:

In normal seawater or marine aquarium water, the bicarbonate greatly dominates all other ions that contribute to alkalinity, so knowing the amount of H+ needed to reduce the pH to 4.5 is akin to knowing how much bicarbonate is present. Aquarists have therefore found it convenient to use alkalinity as a surrogate measure for bicarbonate.

Thanks all for the help!

 

[disc1]

I see. Yes, there is more than carbonate that contributes to alkalinity. Borate for instance. But it is there in very small quantity. Something like 99% of the alkalinity you read is all carbonate if you are measuring seawater. Since we know that, then we use alkalinity as a surrogate measure for carbonate which would be a little more difficult to measure on its own. So alk isn't a measure of carbonates per se, but that's what it is telling you is about carbonates if you are talking about seawater.

BUT, the point is correct. If I make a solution of say ammonia, then the ammonia being a base will increase the alkalinity of the solution. Or if I make a solution of 1mmol/L tartrate, then I will have 2meq/L of alkalinity in that solution because the tartrate is a base (twice).

So alkalinity isn't JUST carbonate, but alkalinity IN SEAWATER is almost all carbonates.


Does that make a little more sense?

 

[nrbelk]

ya, everything clicks now.

For some reason I needed to know the "why" and "how" before I felt like I could trust my test kit.

 

[disc1]

No problem. The whole thing is not very straight forward and I can definitely understand how it can get confusing.