Here's a good article on high pH:
http://www.reefkeeping.com/issues/2005-03/rhf/index.php#6">http://www.reefkeeping.com/issues/2005-03/rhf/index.php#6</a>
[B]Adding vinegar[/B] is another option for reducing pH. It has two actions that lower the pH. The first happens instantly, as the acetic acid releases H<span style="font-size: 1-1px">+</span> to the aquarium water (a process called ionization):
[INDENT] <span style="font-family: Georgia">8. CH<span style="font-family: Arial, Helvetica, sans-serif"><span style="font-size: 1-1px">3</span></span>COOH </span><span style="font-family: Wingdings">à</span><span style="font-family: Georgia"> CH<span style="font-family: Arial, Helvetica, sans-serif"><span style="font-size: 1-1px">3</span></span>COO- + H+</span>
[/INDENT] This effect is shown graphically in Figure 8 (step 1). Then, over a period of time (perhaps hours), the acetate is metabolized by bacteria and other organisms, using up the available oxygen and producing carbon dioxide:
[INDENT] <span style="font-family: Georgia">9. CH<span style="font-family: Arial, Helvetica, sans-serif"><span style="font-size: 1-1px">3</span></span>COO- + O2 </span><span style="font-family: Wingdings">à</span><span style="font-family: Georgia"> 2CO2 + H2O + OH- </span><span style="font-family: Wingdings">à</span><span style="font-family: Georgia"> CO2 + H2O + HCO<span style="font-family: Arial, Helvetica, sans-serif"><span style="font-size: 1-1px">3</span></span>-</span>
[/INDENT] This effect is shown in step 2 of Figure 8. The net result of both reactions is that the acetic acid is converted into carbon dioxide, lowering pH (Figure 8). The real and measured [IMG]http://www.advancedaquarist.com/issues/feb2002/chemistry.htm">alkalinity is reduced</a> a bit by the initial vinegar addition (equation 8), but that loss is exactly replaced when the acetate is metabolized (equation 9). The only concerns with using vinegar are overshooting the pH target by adding too much, and the consumption of oxygen by bacteria metabolizing the acetate. With sufficient aeration or photosynthesis, that O<span style="font-size: 1-1px">2</span> loss is not necessarily a problem, but in some aquaria, adding too much vinegar might cause a significant drop in O<span style="font-size: 1-1px">2</span>.
In another recent test, I bought a commercial bottle of distilled white vinegar (Heinz; Figure 9), and added it to my sump. The sump was stirring well with a large skimmer, but was not circulating through the main display tank during this test. The ~38 gallons of sump water's pH was initially measured at 8.53. After 25 mL of vinegar were added and allowed to mix in for a few minutes, the pH dropped to 8.41. Another 25 mL of vinegar dropped the pH to 8.15. A third 25 mL dose dropped the pH to 7.88. These data serve as the basis for the [IMG]http://www.reefkeeping.com/issues/2005-03/rhf/index.php#recommend">recommendation</a> that I make later in this article of using 1 mL of distilled white vinegar per gallon of aquarium water to achieve an initial pH drop of about 0.3 pH units.
Some solutions to pH problems are peculiar to a specific cause, such as adding [IMG]http://www.reefkeeping.com/issues/2005-01/rhf/index.htm#6">vinegar</a> to limewater, or using less of it. Some general solutions, however, are frequently effective. My recommendations on how to deal with high pH problems are detailed below.
[B]The most benign way to reduce high pH is to aerate the water more[/B]. Whether the aquarium looks well-aerated or not, if the pH is above 8.5 and the alkalinity is not above 4 meq/L, then the aquarium is not fully equilibrated with carbon dioxide in the air. Equilibrating carbon dioxide can be much more difficult than equilibrating oxygen. Air contains very little carbon dioxide (about 350 ppm) relative to oxygen (210,000 ppm). Consequently, a lot more air needs to be driven through the water to introduce the same amount of carbon dioxide as oxygen. Perfect aeration will solve nearly any high pH problem, and will rarely cause any problem of its own.
That said, sufficient aeration is not always easily attained, and other methods can be useful. These other methods are:
[INDENT] [B]A. Direct addition of carbon dioxide[/B]. Bottled soda water (seltzer) can be used to instantly reduce aquarium pH. Be sure to select unflavored soda water, and check the ingredients to be sure it doesn't contain anything that should be avoided (phosphate, etc). Many manufacturers list water and carbon dioxide as the only ingredients.
I recommend adding 6 mL of soda water per gallon of tank water to reduce pH by about 0.3 units. Add it to a high flow area away from organisms (such as in a sump). The local pH where it first is added will be very low. Going about this procedure slowly is better than proceeding too fast. If you do not have a sump, add it [B]especially[/B] slowly. Some soda water may have more, or less, carbon dioxide in it, and the lower the aquarium's alkalinity, the larger will be the pH drop. Also, the higher the pH, the smaller will be the pH drop, because the buffering of seawater declines steadily as the pH drops from about 9 to 7.5.
[B]B. Direct addition of vinegar[/B]. Commercial distilled white vinegar (typically 5% acetic acid or "5% acidity") can be used to instantly reduce aquarium pH. Do not use wine vinegars as they may contain undesirable organics in addition to the acetic acid.
I recommend adding 1 mL of distilled white vinegar per gallon of tank water to initially reduce pH by about 0.3 units. Once again, add it to a high flow area away from organisms (such as in a sump). The local pH where it first is added will be very low. Going about this procedure slowly is better than proceeding too fast. If you do not have a sump, add it [B]especially[/B] slowly. The lower the aquarium's alkalinity, the larger will be the pH drop. Also, the higher the pH, the smaller will be the pH drop, because the buffering of seawater declines steadily as the pH drops from about 9 to 7.5. Remember, there may be an additional, later drop in pH as the vinegar is metabolized to carbon dioxide.
[B]C. Addition of vinegar via limewater[/B]. Commercial distilled white vinegar can be used to reduce tank pH by adding it to [IMG]http://www.reefkeeping.com/issues/2005-01/rhf/index.htm#6">limewater</a> that is subsequently added to the aquarium. Do not use wine vinegars as they may contain undesirable organics in addition to the acetic acid. A [IMG]http://www.reefkeeping.com/issues/2005-01/rhf/index.htm#6">reasonable dose</a> to start with is 45 ml of vinegar per gallon of limewater.
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