Alkalinity

[gbolton]

Can someone explain alkalinity to me. I mean I know what it is but everything I have read has said it is bad if it gets low because the PH and O2 levels can swing. I have a test kit and it always tests high. IS it bad if it is high or is it just bad if it is low?

[mogurnda]

In the simplest terms, alkalkinity is the ability of water to resist change in pH, known as buffering. You measure it by determining how much acid you need to add to cause a pH change. In general, high alkalinity is good, keeping the tank pH stable.

The substances that buffer your artificial seawater (ASW) are usually borate and carbonate. When you add the alkalinity component of two-part additives (like B-ionic), you are adding carbonate ion.

Carbonate has another use, in that it's the other half of the CaCO3 that makes up coral skeletons and snail shells. This means that your tank is consuming Ca and CO3 in equal amounts.

CaCO3 is not very soluble in water, which is the one downside of high alkalinity. Too much CO3 and Ca starts to precipitate out. Which is why you want to keep a balance of the two, 400-450 Ca and 3-4.5 (meq/L) alkalinity. If your test kit doesn't give numerical values, it's worth getting a kit that does. They're pretty cheap.

That was a mouthful. Want to know more? Go here. http://www.advancedaquarist.com/issues/nov2002/chem.htm