pH vs alkilinity

[Rob]

i was wondering what is the difference between pH and alk? iknow that alk makes the ph go up or down. do i want hard water or soft water?

[Plan2Build]

Rob,

pH is a measure of the Hydrogen ion concentration (H+) in water or any solution. The more acidic (more hydrogen in) a solution, the lower the pH...The more alkaline(less hydrogen in), the higher the pH. However, pH and hard vs softwater do not necessarily go hand in hand.

Hard water contains small amounts of dissolved calcium, magnesium and sulfur (well water is hard water). Soft water is formed by the removal of these minerals (e.g. By a water purification facility or water softener).

Your pH is affected by the buffering capacity (or ability to regulate the H+ ion concentration), so if the minerals in the hard water are weak buffers, they will not significantly affect pH.

It would probably be a good idea to use as pure a water as possible so that you know what you are starting with chemically. Also remember that pH is a logarithmic scale. A pH of 7 is neutral...a pH of 8 has ten times less hydrogen ion as 7, and 9 100 times less, etc...

So be careful with those adjustments...........

Just my $0.02

P2B

[Plan2Build]

Rob,

I just found this link that may give a more precise explanation:

http://saltaquarium.about.com/gi/dyn...%255Fchem1.htm

Here is an excerpt:

pH. The degree to which a solution is acid or alkaline is the pH of the solution. Pure water, the standard reference point for many chemical measurements, has a pH of 7, and is said to be "neutral." A solution with a pH less than 7 has more hydrogen ions than pure water, and is said to be "acidic," while a solution with fewer hydrogen ions than pure water has a pH greater than 7, and is said to be "alkaline" or "basic." Hydrogen ions are among the most important chemical species, involved in all kinds of reactions that take place in aquarium waters.

Ions are charged molecules. Hydrogen ions carry a positive charge, as signified by the chemical shorthand for this ion, "H+." Ions can exist only as pairs, with each positively charged ion matched by a corresponding negatively charged one, so that the overall charge always remains at zero. In pure water, the hydrogen ions are balanced by hydroxyl ions (OH-). Just as adding hydrogen ions to the water causes the pH to decrease, adding hydroxyl ions has the opposite effect, making the solution more basic. Adding acid to a basic solution, or vice versa, results in some of the ions recombining to form pure water. This is called a "neutralization reaction."

Alkalinity. The degree to which a solution maintains its pH when acid is added is the alkalinity of the solution. Related terms used in reference to aquariums, are "carbonate hardness," and its German equivalent, "KH." In practice, these terms are used interchangeably, but in reality total alkalinity in seawater is slightly higher than carbonate hardness. This is because the latter is a measure of only the contribution of carbonate (CO3-2) and bicarbonate (HCO3-) to total alkalinity. Various other negatively charged ions, such as borate (BO33-) and hydroxides (OH-) contribute to the total.

Alkalinity is measured in milliequivalents per liter (meq/l). To understand the derivation of this term, and to better understand the concept of alkalinity, it is important to consider the neutralization reaction. The general formula for a neutralization reaction is written as follows: H+ + OH- ---> H2O


P2B