Reef Chemistry Question of the Day #10

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #10

Understanding the relative amounts of different things in a reef aquarium can help understand some of the processes taking place.

Please rank order, from highest concentration to lowest concentration, the following ions that are present in a typical reef aquarium.

A. Carbonate
B. Bicarbonate
C. Calcium
D. Phosphate

For example, if you thought carbonate was highest and phosphate the lowest, you might write A>C>B>D.

Good luck.

 

[lakeviewink]

C>b>a>d

 

[Zero Nitrates]

C>a>d>b

 

[Kyuss414]

C<A<B<D

Although if you asked me 8-9 months ago when my tank was only a couple months old, I might have put D in first place :mmph:

 

[jt17]

D<b<a<c

 

[beaslbob]

depends on ph

 

[Randy Holmes-Farley]

Good work. I think the winner is lakeviewink!

The bicarbonate/carbonate distinction can be a tricky one, and the different units between the way we measure "alkalinity" (bicarbonate and carbonate) and calcium may make that comparison tricky.

The answer is

C > B > A > D
Calcium > Bicarbonate > Carbonate > Phosphate


The answer does depend on pH, but unless the pH is above about 8.9, there is more bicarbonate than carbonate.

The importance of calcium being a lot higher than bicarbonate (by about a factor of 4-5 or so when referring to the number of ions present) is that if you are using a balanced calcium and alkalinity additive system (limewater/kalkwasser, CaCO3/CO2 reactor, two/three part system with both main parts equal), then underdosing always results in alkalinity dropping noticeably first, and when overdosing, alkalinity always rises noticeably first.

 

[luxauterna]

nice. I love these questions.

 

[Randy Holmes-Farley]

nice. I love these questions.

I'm glad you like them.

 

[lakeviewink]

Haha thanks. I thought maybe I was mistaken after everyone else's answers were different but I was pretty sure I had it right.
I had an older Seachem test for both bicarbonate and carbonate seperately and I remembered the carbonate was less by a ratio of around 2:1

 

[Randy Holmes-Farley]

Haha thanks. I thought maybe I was mistaken after everyone else's answers were different but I was pretty sure I had it right.
I had an older Seachem test for both bicarbonate and carbonate seperately and I remembered the carbonate was less by a ratio of around 2:1

Excellent. Don't bow to peer pressure, especially in chemistry.

 

[Kyuss414]

Nice job!