Anyone testing for CO2 in a reef aquarium? I added some phenolphthalein to a sample and the result suggests CO2 is present. Awaiting NaOH titrant to quantify.
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Yep. The "CO2" in the seawater is mostly of form HCO3 bicarbonate with lesser amounts of CO3 carbonate ...Wouldn’t you expect some dissolved co2? I think Gibbs feee energy states it should tend towards forms of carbonate... but I haven’t looked at those equations in forever. But there has to be some level for it to reach equilibrium.
Yep, the equilibria at reef-tank pH is strongly shifted towards bicarbonate/carbonate. If you want to get in deep into the chemistry, this section of a course's notes might help.Wouldn’t you expect some dissolved co2? I think Gibbs feee energy states it should tend towards forms of carbonate... but I haven’t looked at those equations in forever. But there has to be some level for it to reach equilibrium.
Anyone testing for CO2 in a reef aquarium? I added some phenolphthalein to a sample and the result suggests CO2 is present. Awaiting NaOH titrant to quantify.
Yep, the equilibria at reef-tank pH is strongly shifted towards bicarbonate/carbonate. If you want to get in deep into the chemistry, this section of a course's notes might help.
Oh my god! This makes me sooo excited. I can’t wait to have all of this for my tank.Here's my daily cycle of CO2 and O2 according to Mindstream:
Thanks all for the replies. I was using a Seneye device to measure pH in the tank. When the sensor expired, I began using an American Marine pH monitor with a new (but not temperature compensated) probe. The pH with the Seneye was 8.1 but was reported to be less than 8 with the American Marine unit. I confirmed the low pH with a second non-ATC probe. I ordered a new pH probe (ATC) for my Hach data logger and the pH was a little higher but still below 8. I could take the easy way out and put a soda lime CO2 scrubber on the intake to the skimmer. But that's never been me. And I wonder why I constantly feel overloaded. LOL. The tank management practices changed about the time I began to see pH issues (heavy live green water additions, skimmer running only at night, etc.) As soon as the CO2 titrant arrives, I'll get busy looking at CO2, dissolved oxygen, total N & P, acid hydrolyzable P, nutrients, etc. In the meantime, most corals are showing good growth rates (some of the Cyphastreas were growing over their epoxy bases within days.)
Always, if you have a sensitive enough technique.Wouldn’t you expect some dissolved co2? I think Gibbs feee energy states it should tend towards forms of carbonate... but I haven’t looked at those equations in forever. But there has to be some level for it to reach equilibrium.
Awaiting NaOH titrant to quantify.
Dana, I'm confused about how you intend to titrate CO2 using NaOH. Isn't a strong acid usually used for titrating the carbonate alkalinity in seawater down to the carbonic acid endpoint, rather than titrating up to the phenolphthalein endpoint? Am I missing something? I'm also not sure I understand your phenolphthalein test comment. Did the sample fail to turn pink, indicating a pH lower than the phenolphthelein endpoint due to excess CO2? Is your thought process that you can titrate the excess carbonic acid with the NaOH to the phenolphthalein endpoint as a measure of the excess carbonic acid? Again, I'm confused, and not at all sure what your thought process is here. Please elaborate, so I can better understand.As soon as the CO2 titrant arrives
The chemists at Hach can explain better than I. Go to hach.com, search for 'CO2 test digital titrator' and look in 'Downloads.' There the procedure (applicable to seawater) is outlined. I'm not a chemist by trade, so I'm relying on their veracity.Dana, I'm confused about how you intend to titrate CO2 using NaOH. Isn't a strong acid usually used for titrating the carbonate alkalinity in seawater down to the carbonic acid endpoint, rather than titrating up to the phenolphthalein endpoint? Am I missing something? I'm also not sure I understand your phenolphthalein test comment. Did the sample fail to turn pink, indicating a pH lower than the phenolphthelein endpoint due to excess CO2? Is your thought process that you can titrate the excess carbonic acid with the NaOH to the phenolphthalein endpoint as a measure of the excess carbonic acid? Again, I'm confused, and not at all sure what your thought process is here. Please elaborate, so I can better understand.