Trying to figure something out here... Alk vs Carbonate

[tbrown]

Ok, so first, I know people are going to cringe because, yes, I am relying on test strips to get me a ballpark eyeball on my system.

So the test strips I'm using have Alk and Carbonate Hardness. My Carbonate is right in the middle of the "Good" range for saltwater (around 100ppm) but my alkalinity is showing super low (approximately 50ppm). Some people say Alk and Carbonate are basically the same thing. If I'm trying to raise the Alk without raising Carbonate I need to raise Bicarbonate, correct?

Calcium is 420
Magnesium is 1475

 

[Randy Holmes-Farley Verified Community Expert]

You are not measuring carbonate. That's not possible. You are measuring carbonate hardness or carbonate alkalinity.

Carbonate hardness and total alkalinity are nearly identical in seawater (alkalinity from borate is the main difference), and 100 ppm calcium carbonate equivalents is quite low and I'd ignore that recommendation. It's about 5.6 dKH.

I do not think strips are a useful way to measure alk in seawater. I cannot even imagine how the manufacturer thinks it would work. lol

You also have no control over bicarbonate vs carbonate in the water, except by changing the pH. They interchange instantly and are in equilibrium with each other based on the pH (low pH is more bicarbonate).

 

[tbrown]

You are not measuring carbonate. That's not possible. You are measuring carbonate hardness or carbonate alkalinity.

Carbonate hardness and total alkalinity are nearly identical in seawater (alkalinity from borate is the main difference), and 100 ppm calcium carbonate equivalents is quite low and I'd ignore that recommendation. It's about 5.6 dKH.

I do not think strips are a useful way to measure alk in seawater. I cannot even imagine how the manufacturer thinks it would work. lol

You also have no control over bicarbonate vs carbonate in the water, except by changing the pH. They interchange instantly and are in equilibrium with each other based on the pH (low pH is more bicarbonate).

Thanks for the response!

So if I need to raise Alk and my pH is 8.4 I should use a bicarbonate alkalinity rather than carbonate alkalinity, correct?

 

[Randy Holmes-Farley Verified Community Expert]

Thanks for the response!

So if I need to raise Alk and my pH is 8.4 I should use a bicarbonate alkalinity rather than carbonate alkalinity, correct?

You mean to dose? Most people do not have pH above 8.4 without dosing high pH additives, and it may be inaccurate, but if true, then sodium bicarbonate 9grocery store baking soda) is likely what I'd use to boost alk.

 

[tbrown]

You mean to dose? Most people do not have pH above 8.4 without dosing high pH additives, and it may be inaccurate, but if true, then sodium bicarbonate 9grocery store baking soda) is likely what I'd use to boost alk.

Thanks! I've confirmed my pH through multiple test kits. All of my tanks run in the mid to upper 8s for pH - even my freshwater tanks.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks! I've confirmed my pH through multiple test kits. All of my tanks run in the mid to upper 8s for pH - even my freshwater tanks.

Well, I'm skeptical. pH strips are not a good way to judge pH in seawater. Upper 8's are never attained without massive high pH alk supplement overdose, and mid 8's usually only with normal use of high pH supplements (or low aeration).

 

[Tankkeepers]

Ok, so first, I know people are going to cringe because, yes, I am relying on test strips to get me a ballpark eyeball on my system.

So the test strips I'm using have Alk and Carbonate Hardness. My Carbonate is right in the middle of the "Good" range for saltwater (around 100ppm) but my alkalinity is showing super low (approximately 50ppm). Some people say Alk and Carbonate are basically the same thing. If I'm trying to raise the Alk without raising Carbonate I need to raise Bicarbonate, correct?

Calcium is 420
Magnesium is 1470

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

reefs.com