Will we ever see an Alkalinity Probe?

[Nexenn]

Doesn't that just tell you what your bicarb is though?

CO2 + h2O <--> H2Co3 <---> H+ + HCO3-

So if you know CO2 and H+ then you know HCO3-?

 

[Randy Holmes-Farley]

It can tell you both bicarbonate and total alkalinty (and carbonate if you wanted that), and either is adequate for reefers.

Using equation 2 in this article (it doesn't copy and paste well), for example, allows one to solve for alkalinity knowing pH (or H+) and carbon dioxide (as pCO2):

The Relationship Between Alkalinity and pH.
http://www.advancedaquarist.com/issues/may2002/chem.htm

K1, K2, and KH are all known (but vary with salinity if you are not at 35 ppt).

 

[jcolletteiii]

I've thought about this a little bit as well, to the point of Googling 'dissolved CO2 monitor', etc. Unfortunately, I've found that for what I was thinking, the cost would be very high. My chemistry is a bit week, but couldn't you hypothetically use dissolved O2 as a proxy for [CO2]? Dissolved O2 monitors are much cheaper and more readily available than CO2 monitors. Our tanks can be though of as being representative of sea surface conditions - except that they are in equilibrium with our house ambient air - concentrations of gas in solution will depend on the solubilities of each gas, salinity, and temp. I believe [N2] and [Ar] are relatively constant in water of known temperatures, so if salinity, temp, [N2], [O2], and [Ar] are known (or can be surmised), can't [CO2] be calculated pretty easily? This is kind of a workaround, but perhaps there is potential? It seems that if the dissolved [CO2] could be detected or calculated more economically, an alk controller would be fairly straight forward.

 

[Randy Holmes-Farley]

I've found that for what I was thinking, the cost would be very high. My chemistry is a bit week, but couldn't you hypothetically use dissolved O2 as a proxy for [CO2]?

No, dissolved O2 and CO2 move independently in a reef tank. During the day, when the tank is photosynthesizing, O2 rises and CO2 falls. The same happens at night in reverse due to respiration. Both have been tracked in reef tanks and the effect is substantial.

 

[blairk]

working in a hospital lab i have access to a bloog gas analyzer, i can get
pCO2, ph and bicarbonate results, can i use the results from this to determin my alk?

 

[Randy Holmes-Farley]

From pH and PCO2 you can get alkalinity. I doubt it is worthwhile going to all that trouble for a simple alk measurement, but you could use an equation like equation 2 in this article:

http://www.advancedaquarist.com/2002/3/chemistry

From pH and bicarbonate, you can also get alkalinity. Bicarbonate is close to alkalinity, but you need to add the contribution for carbonate too. You do that in an equation like that below, where you also need to calculate the carbonate concentration from the bicarbonate and the pH by a calculation, a table, or a graph like the one shown below.

 

[laud]

To say this isn't possible is like saying there is no way you test a diabetics blood sugar by the transference of glucose through the interstitial fluid in the skin cells. But alas! Since this thread was written, it has been achieved.

I know this is an old thread, but MAN if I could put a probe into my tank and see the alk swings, my quality of life and tank inhabitants lives would be greatly increased.

 

[Jgoal55]

with some alk issues of late, a google search led me here.

So, it's 2011....this thread started in 2008. Randy, Any luck in three years in developing a continuous alk tester/probe? Even one that tested once or twice a day would work for me.

Thanks.

 

[tonyespinoza]

Started the thread years ago... still waiting!

 

[FiShScaLe]

http://www.bulkreefsupply.com/store/review/product/list/id/1761/category/329/

I was going to order this they sell a reliable phosphate test kit. Is this not the same thing?

 

[Jgoal55]

Ive heard great reviews about those Hannah testers and overall very affordable....but I think what most everyone on this thread is asking for is continuous alkalinity monitoring.

The Hannah kits are just a fancier and more accurate version of your typical reagent based Salifert type kit.

 

[FiShScaLe]

ahhh I see so something like a ph or salinity probe that will give a constant reading....that would be great wouldnt it

 

[Jgoal55]

exactly.....yes it would

 

[Eel Freak]

I was poking around the vast world of the internet today and came across this. It's from 1974, so I'm not 100% sure of the modern-day scientific applicability...

Not too sure where the company you were working with is at right now, but I thought this was interesting nonetheless. Perhaps you could work with them to develop a bicarbonate ion-selective electrode...

 

[notclear]

Any new update on this kind of probe?

This one is not for aquarium use I believe :

http://www.nivetec.com.br/novosite/docs/catalogo/Hach Alcalinidade APA6000.pdf

 

[Randy Holmes-Farley]

That link doesn't work, but there are no bicarbonate ISE probes suitable for use in seawater that I have ever seen. I've not seen any commercial bicarbonate electrodes, even for freshwater.

 

[notclear]

Thanks.

I just tried the link again and it worked for me.

 

[Randy Holmes-Farley]

Well, all I get is:

Oops! Google Chrome could not find www.nivetec.com.br

 

[notclear]

That's strange, I tried again at home, both with IE9 and Chrome. They both worked.

 

[Randy Holmes-Farley]

OK, that works now. That is not a probe. It is just an automated version of the standard titration used in typical alkalinity kits. These have been around a while.