View Full Version : Do digital ALK meters exist?

01/26/2006, 09:53 AM
I love the convinience of my digital PH and salinty meters, I know digital Ca meters are unreliable, but are there digital ALK meters?

01/26/2006, 09:58 AM
I dont know of one and would not think it would be cost effective IMO, there are a lot of parameters that would have to be detected to determine alk, bicarbonate & carbonate concentration and pH & pOH being the biggest contributors.

There is also Borate, Silicate, Phosphate(s) that contribute although I do not know how much they actually contribute

If there is such a thing I would be interested though.

01/26/2006, 10:11 AM
see here: http://www.advancedaquarist.com/issues/feb2002/chemistry.htm

Section: Why is Alkalinity Important?

Now that we know what alkalinity is, we can understand why it is an important measure for reef tanks. Corals and other organisms deposit calcium carbonate in their skeletons and other body parts. In order to do this they must generate calcium and carbonate at the surface of the growing calcium carbonate crystal. While it is far beyond the scope of this paper to describe this process, it is readily apparent that if corals deposit these chemicals, they are using them up from the water that they inhabit. So, if that’s the case, why not just measure carbonate as we do calcium?

Well, there are two answers. The first is that there is no simply way to measure carbonate with a kit without doing a pH titration as an alkalinity test kit does. Second, corals may actually use bicarbonate instead of carbonate as their ultimate source of carbonate (which they split into H+ and CO3--). If we could easily measure bicarbonate, we’d probably be doing just that. Unfortunately, we can’t do either of those things easily.

So what we are doing is using a very simple alkalinity test as a surrogate measure for bicarbonate and carbonate. Since these two substances comprise the great majority of alkalinity in seawater, it is safe for most people to equate alkalinity with "availability of bicarbonate and carbonate for my corals".

There are, however, some important caveats to that equation. Some of these were described above, such as salt mixes that have excessive borate. Such complications make it difficult to know how much of the measured alkalinity is bicarbonate and carbonate, and thus it is difficult to know if you are satisfying the needs of the corals [Hence the unusually high alkalinity recommendations by Seachem].

Randy Holmes-Farley
01/26/2006, 02:57 PM
No, there is no alk meter/probe. I don't think there ever can be as it is not a thing in solution, but the result of how much acid it takes to drop the pH to 4.2 or so.

One day there may be a bicarbonate meter, which could be just as useful, or more so than alkalinity, but there is none available today.

01/26/2006, 06:55 PM
I don't think there ever can be as it is not a thing in solution, but the result of how much acid it takes to drop the pH to 4.2 or so.

Interesting, can you explain how Saliferts test works? You put the two drops in, which turns the water greenish blue. Then add the other part dropwise until the color changes.
Are we lowering the ph of the sample to 4.2? If so, why cant they make their PH test kits more accurate, or on the other hand, how accurate are the Alk tests. I always thought them to be very accurate. Of course my opinion is based on the night and day difference between the green color and the change to yellow, or whatever it is.

I run Alk tests more than anything, couple times per week lately.

01/26/2006, 06:59 PM
Thanks, and some interesting points in the replies.

01/27/2006, 12:56 AM

We could do that but most Alk kits are more than accurate enough for our purposes. In fact, you would get a much more accurate view on the carbonate/bicarbonate components by using a digital probe (calibrated properly) and drawing your complete titration curve while lowering the Ph of the solution. However, it is simply unnecessary to do this every time we want to check Alkalinty. Doing a complete titration and drawing the curve is a good excercise to become more familiar with the carbonate/bicarbonate/alkalinity relationship.

Randy Holmes-Farley
01/27/2006, 06:35 AM
Are we lowering the pH of the sample to 4.2?

Yes. All total alkalinity kits are actually pH titrations, where acid is added and the colored indicator shows when the pH goal has been reached. The exact pH of the alkalinity endpoint does not impact the measured alkalinity very much because the pH is changing pretty fast with each drop near the endpoint. I show a pH titration to get alkalinity in the article linked above. :)

01/27/2006, 12:41 PM

No, there is no alk meter/probe.

Sure there are, they are quite common in the water/wastewater industry. BUT, they are self-automated titrators :D They are big toys, some the size of an avg TV. Many also act as controllers releasing buffers. HACH make one, the APA 6000 Alkalinity Analyzer. My favorite meter company Yokogawa, still does. You wll need to sell your car :lol:


IIRC there also ISE CO2/CO3 probes but I do not know how they work> check Cole-Parmer

Randy Holmes-Farley
01/27/2006, 01:12 PM
Yes,one can do an automatic titration. :lol:
You can also hire Habib to stand by your tank and use his kit every 15 seconds. :D

01/27/2006, 01:44 PM
You can also hire Habib to stand by your tank and use his kit every 15 seconds.

Yes and that should be be cheaper :D