Carbonate vs Bicarbonate

[Coral Reef To Classroom]

Scientists have reported that increased CO2 in the ocean is causing a decrease in available carbonate for corals. These same chemical reactions also cause an increase in bicarbonate. It is believed corals expend more energy while using bicarbonate as opposed to carbonate to build their skeletons. Can this information be applied to our tank? If pH does not impact the choice, shouldn't we dose carbonate and not bicarbonate to our reef tank?

 

[Naekuh]

Calcium Carbonate = Soda Ash.
Calcium Bicarbonate = Baking Soda.

If the top had very little impact on pH, i would see no point in Baking Soda.

I think thats why we have the two, if you need to raise pH or not along with Alk.

 

[Coral Reef To Classroom]

It appears the consensus is that it is okay to use bicarbonate unless you are trying to raise your pH. Because of its ease of use, it makes sense to choose it over carbonate. My question is, Can we promote better coral health by using carbonate instead of bicarbonate?

 

[Randy Holmes-Farley Verified Community Expert]

Scientists have reported that increased CO2 in the ocean is causing a decrease in available carbonate for corals. These same chemical reactions also cause an increase in bicarbonate. It is believed corals expend more energy while using bicarbonate as opposed to carbonate to build their skeletons. Can this information be applied to our tank? If pH does not impact the choice, shouldn't we dose carbonate and not bicarbonate to our reef tank?

I am not sure that what you are saying is exactly correct (the part about using bicarbonate vs using carbonate) but lowering pH certainly does shift the alk toward more bicarbonate and less carbonate.

Bicarbonate and carbonate have a ratio in seawater that is fixed only by pH and salinity. You cannot control those two just by what you dose. You can control them by pH and by total alkalinity.

 

[Randy Holmes-Farley Verified Community Expert]

It appears the consensus is that it is okay to use bicarbonate unless you are trying to raise your pH. Because of its ease of use, it makes sense to choose it over carbonate. My question is, Can we promote better coral health by using carbonate instead of bicarbonate?

I don’t agree. It is not the consensus that bicarbonate is better/easier to dose, or that it makes sense to dose it over carbonate or hydroxide.

 

[Randy Holmes-Farley Verified Community Expert]

Calcium Carbonate = Soda Ash.
Calcium Bicarbonate = Baking Soda.

If the top had very little impact on pH, i would see no point in Baking Soda.

I think thats why we have the two, if you need to raise pH or not along with Alk.

Switch those names to sodium instead of calcium:

Sodium Carbonate = Soda Ash.
Sodium Bicarbonate = Baking Soda.

 

[Naekuh]

Switch those names to sodium instead of calcium:

Sodium Carbonate = Soda Ash.
Sodium Bicarbonate = Baking Soda.

ack thanks for the fix randy... i am lacking caffine this morning.

 

[Coral Reef To Classroom]

I don’t agree. It is not the consensus that bicarbonate is better/easier to dose, or that it makes sense to dose it over carbonate or hydroxide.

Sodium carbonate is much easier to get and less expensive which is why I would think it would be more popular to use. I have often read "just use sodium carbonate it doesn't decrease pH by that much so no big deal". So I guess my next question is, If my ph is 8.3, does bicarbonate become carbonate in my tank?

 

[Dom]

It appears the consensus is that it is okay to use bicarbonate unless you are trying to raise your pH. Because of its ease of use, it makes sense to choose it over carbonate. My question is, Can we promote better coral health by using carbonate instead of bicarbonate?

Now, I thought it was the other way around.
You use bicarbonate (baked baking soda) to give your pH a boost.

 

[Coral Reef To Classroom]

Sorry my post has a typo. I did mean sodium bicarbonate.

 

[Tripod1404]

Sodium carbonate is much easier to get and less expensive which is why I would think it would be more popular to use. I have often read "just use sodium carbonate it doesn't decrease pH by that much so no big deal". So I guess my next question is, If my ph is 8.3, does bicarbonate become carbonate in my tank?

It will reach to an equilibrium where it exists in both forms based on pH, temp, salinity etc.

 

[Randy Holmes-Farley Verified Community Expert]

You have no control over the ratio, except by pH and salinity, as noted above.

I have diy recipes that use bicarbonate, carbonate, and hydroxide. All work fine and just have different effects on pH when added. The carbonate recipe is by far the most popular because it provides the pH boost most want. Hydroxide has an even bigger pH boost, and us slowly gaining in popularity since it is a much newer recipe.

 

[Randy Holmes-Farley Verified Community Expert]

You can easily buy sodium carbonate (say, from bRS) or you can make it from baking soda by simply baking it in a home oven first.

 

[Coral Reef To Classroom]

I dose calcium hydroxide but need a little boost for alkalinity which I have used both sodium carbonate and sodium bicarbonate on different occasions. I have been wondering for awhile now if I would be better off using sodium carbonate even though I didn't need the pH boost.

 

[Randy Holmes-Farley Verified Community Expert]

I dose calcium hydroxide but need a little boost for alkalinity which I have used both sodium carbonate and sodium bicarbonate on different occasions. I have been wondering for awhile now if I would be better off using sodium carbonate even though I didn't need the pH boost.

If you do not want the pH higher, then there's no advantage to dosing carbonate over bicarbonate.

On the topic of exactly why pH impacts coral calcification rates, I think that is an unresolved question at the molecular level.

The two potential mechanisms are:

1. Take up bicarbonate and secrete a proton.
2. Take up carbonate.
3. Both 1 and 2 happening in the same organism.

Distinguishing those is not really possible by simple observation of coral response to pH, since both become easier as pH rises at fixed alkalinity, and both become easier as total alkalinity rises.

It would, IMO, take a detailed biochemical analysis of the uptake and secretion transporters present in corals and when and how they are regulated. I've not seen that done at the level needed, and it may vary between organisms.

 

[Coral Reef To Classroom]

Yes and if they are taking up bicarbonate and secreting a proton they expend energy to do so. And now the free proton potentially drops pH. I couldn't help but wonder if in the confines of our tank, adding bicarbonate would actually be having negative effects on our corals. Maybe I am just over thinking things. Thank you for your help.

 

[Randy Holmes-Farley Verified Community Expert]

Yes and if they are taking up bicarbonate and secreting a proton they expend energy to do so. And now the free proton potentially drops pH. I couldn't help but wonder if in the confines of our tank, adding bicarbonate would actually be having negative effects on our corals. Maybe I am just over thinking things. Thank you for your help.

Yes, you are overthinking it, IMO. Folks have used all of these alk dosing methods with essentially equal success for decades.

Both of the processes I identified above have the same net effect of consuming carbonate.

Replacing that carbonate with carbonate has a net overall pH effect of zero, despite having a pH boost when added and a pH decline when organisms consume the carbonate. Replacing the alk with bicarbonate has a net effect of lowering pH, both when added and when carbonate is consumed, but does not cause any other issue.