My Reef Chemistry Notes

[sihaya]

While I'm busy avoiding doing everything else I should be doing, I thought I'd share my reef chemistry "cheat sheet" with you all.

For beginners who don't remember much chemistry:
Broken down to basics, we're just talking about charged particles (ions) in water. The ones we care a lot about are H+(hydrogen), Na+(sodium), Ca2+(calcium), OH-(hydroxide ion), Cl-(chloride), C(O3)2- (carbonate), H(CO3)- (bicarbonate). The positively charged particles match up with negatively charged particles to make different chemicals. It might sound a little complicated, but don't over think it. It's kinda like putting magnetics together...

This chart shows how the different combinations of positive and negative ions give us our basic inorganic additives:

So where do these ions come from? Well, check it out...


Two things I had to learn on my own because my LFS couldn't tell me...

1. What's exactly is the difference between pH and alkalinity?

pH is short for "power of Hydrogen." It's the concentration of H+ in a solution (aka acidity).

Alkalinity is a more complicated beast. In function, it's a buffer. Buffers inhibits sudden changes in pH over a certain range. The ability of the buffer to prevent sudden changes in pH is called a "buffer capacity." As we usually use the term in the hobby, alkalinity is the "buffer capacity" of our water. Bicarbonate and carbonate are the major contributors to alkalinity. They're not the only contributors, but in our tanks, they're by far the most important. (The contribution of borate is an interesting topic, but I don't want to give you all a headache. If you're curious, here's RHF great article on that: http://www.advancedaquarist.com/issues/dec2002/chem.htm)

2. What do the alkalinity tests actually test for?

Most don't test for any one compound. Most of them are titration kits that give you an idea of buffer capacity by finding out how much acid it takes to break the buffer (the point at which the buffer can no longer inhibit the change in pH). For more info on all that: http://www.advancedaquarist.com/issu.../chemistry.htm

[Poseidon]

Great info Sara, I hope you don't mind me making this a STICKY!

[sihaya]

Great info Sara, I hope you don't mind me making this a STICKY!

If you really think it's that helpful, of course not! But come on, I'm blushing!

[sihaya]

Oops, I forgot to mention the Boron/Borate issue too:

About Boron:

It exists in sea water as Boric Acid (B(OH)4)- and Borate, B(OH)3. Which are a weak acid and its conjugate base. Y'all know what that means right? It's a BUFFER! And just like with the bicarbonate/carbonate duo, it affects alkalinity.

Now, this gets really geeky reefers all excited because artificial salt mixes are often much higher in Borate/Boric Acid than natural sea water. So, when they measure their alkalinity with a test kit (which almost certainly only measures levels of bicarbonate/carbonate), they might not be getting a very accurate measure of the tanks true buffer capacity.

For all the hairy details: Chemistry and the Aquarium