Not all carbonates are the same?

[Maximitsurugi]

Hey @RandyHolmesFarley. I use the NaOH mixture for Alk but recently I've been hearing that not all carbonates are the same, meaning corals might prefer, for example, baking soda over caustic soda. I thought they all ended up as the same thing?

 

[thatmanMIKEson]

Hey @RandyHolmesFarley. I use the NaOH mixture for Alk but recently I've been hearing that not all carbonates are the same, meaning corals might prefer, for example, baking soda over caustic soda. I thought they all ended up as the same thing?

I was wondering this too, about supplemental with kalk along with 2 part for the corals that prefer it that way over say soda ash..good question!

 

[mdb_talon]

I may be completely wrong and look forward to any input from Randy, but my understanding is it does not matter from the corals perspective the source of your carbonates with the examples given. As I understand it (and again may be wrong) corals need carbonate alkalinity and that is what matters... but is not the same as total alkalinity that may measure other things like boron for example. I believe though that for our purposes carbonate alkalinity would almost always be close enough to total alkalinity that it is not really relevant. I dont think the source of that carbonate alkalinity is really relevant though. Look forward to finding out if I actually have that right though.

 

[Dennis Cartier]

I believe the common consensus among marine scientists is that corals primarily uptake bicarbonate. That being said, all the forms of carbonate dosing, including hydroxide and carbonate, can provide the needed bicarbonate as they get converted from hydroxide to carbonate and then to bicarbonate while up taking CO2 from the water column, and giving a rise in pH.

So I think the type of carbonate is not important.

Unless your pH is already elevated, and then the type, and effect on pH, may be more relevant (to you).

 

[Randy Holmes-Farley Verified Community Expert]

There are three forms present in seawater:

1. Carbonic acid. H2CO3 very litttle of this is present
2. Bicarbonate. HCO3- this one dominates at all reef tank pH below 8.9; bicarbonate = carbonate at pH 8.9)
3. Carbonate. CO3--. This one is a small fraction of the total, and the lower the pH, the smaller the fraction.

At any given pH, no matter what you dose, the ratio of bicarbonate to carbonate is the same. It only depends on pH (and salinity)

The carbonate alkalinity (which is close to the total alk we measure) is:

carbonate alk = bicarbonate + 2 x carbonate

Thus if you know the pH and the alkalinity, you can know both the bicarbonate and the carbonate, defined mathematically, regardless of what you actually dosed to get there.

Thus, one does not need to take into account what you are dosing, just what the pH is, and what the alkalinity is.

Hope that helps

 

[thatmanMIKEson]

Thats a good one, I think deeper into it when you say it only depends on PH and salinity....