pH

From Microcosm Aquarium Explorer

What Is pH?

pH is a measure of the concentration of hydrogen ions [H+] and is expressed as a negative log. That is, the negative log of the concentration of hydrogen ions -log[H+].

In lay terms, it is the measure of how acidic or basic the water is. pH ranges from 0 to 14, where 7 is said to be neutral. Any value below 7 is acidic and any value above 7 is basic.

The pH of natural seawater is mildly basic and ranges from 8.0 to 8.4.

Why Test pH

In the home aquarium, a pH of 8.3 to 8.4 is recommended. Levels lower than 8.2 or higher than 8.6 may indicate undesirable conditions in the aquarium. Further, staying in the upper end of the natural range for pH helps inhibit the growth of undesirable filamentous algae.

How To Test pH

pH may be tested by adding an indicator solution to a water sample, using dip sticks or papers, or by the use of electronic devices.

In general, I do not recommend the electronic meters for the beginning or even intermediate hobbyist. Such devices need to be constantly calibrated and cleaned to ensure accuracy. This not only becomes a time-consuming hassle, but most electronic metering instruments are relatively expensive. Some argue that money can be saved because you no longer need to buy reagents and replace test tubes. Ah, true—but with electronic devices you are forever buying calibration solutions.

In my opinion, the far simpler way to test pH is with liquid test kits. The indicator turns the sample a color. The color of the resulting liquid is then compared to standard colors. The pH of the sample will be the number indicated by the closest color match. It is best to test pH at approximately the same time of day. The pH of aquarium water fluctuates slightly throughout the 24-hour period in relation to the timing of light and dark periods. A graph of these daily fluctuations reveals a pattern that is more or less the same for any given day. Because of this, it is useful to test at or near the same time every day. Testing at a consistent hour will place the results of each test near the same point of the pH curve, making test comparisons more useful.

Proper pH Level

pH should not be allowed to fall below 8.2 nor rise above 8.6. The ideal pH range for calcification is 8.4 to 8.45. For “fish-only” aquariums, values between 8.3 and 8.5 are acceptable.

Record pH in Your Log

Once you have obtained the result of the pH test, record it in your log and on your graph. Note whether or not the graph looks as it should. Are the fluctuations in the graph getting larger? Increasing fluctuations in the pH graph could indicate a problem with alkalinity.

How To Adjust pH

Recall that pH is a negative log of the concentration of hydrogen ions. Therefore to change or correct pH, we would need to change the concentration of these hydrogen ions in the aquarium water. If the pH is too low, then we have too many hydrogen ions and if the pH is too high then we do not have enough of them. In practice, this involves adding an acid solution if pH is too high and a basic solution like sodium bicarbonate if the pH is too low. There are many preparations on the market for accomplishing these adjustments.

Marine, or seawater, buffers are basic mixtures that contain additional elements for pH stabilization. I should caution here that adding acids to marine aquariums is not recommended. One author (Theil), for instance, suggested adding seltzer water to the aquarium to lower pH. I have never personally tried this method though it would no doubt work. My concern would be that the carbon dioxide and in some cases phosphoric acid in the beverage would become nutrients for pest algae. Additionally, I’ve yet to find a bottle of sparkling water with dosing instructions on the label for lowering the pH of my aquarium.

A much better method for lowering pH would be to perform a partial water change.

— Carl DelFavero
Reference: Aquarium Keeping and Rescue