Properly Maintaining the pH in a Freshwater Aquarium
Published April 07, 2008
Written by Katherine Barrington
Learn how about pH and how to properly maintain it in a freshwater aquarium.
The pH scale is used to measure the degree to which your aquarium’s water is acidic, alkaline, or neutral. The scale ranges from 0 to 14 with 0 being the most acidic, 7 being neutral, and 14 being the most basic. Most fish thrive in a pH of 6.4-7.8. However, there are exceptions. This article will introduce some of the main concepts in adjusting and maintaining a proper pH for your fish.
Consistency, Consistency, Consistency
People often become overly worried about attaining an exact pH. For example, someone may have heard that their specific fish prefers a pH of 7.2. They, therefore, may try to do everything under the sun to get their aquarium’s pH to exactly this number. In most cases, however, this is completely unnecessary. Fish are remarkably flexible and they will adapt to a wide range of pH in most cases.
It is much more important that you maintain a consistent pH. While a fish that “prefers” a pH of 7.2 will more than likely live in perfect health with a pH of 6.7, that same fish will become extremely stressed if you have a pH swing of 0.3 over the course of a day. Therefore, instead of trying get your pH to an exact value, try to keep the pH fairly constant (by constant, I mean no more than a 0.2 change in the pH during a 24 hour period) as this is considerably more important.
As a side note, some species are very particular about the pH when they breed. If you plan to breed a certain species, research the range of pH it finds acceptable to breed in. Some species are very forgiving, while others have a very tight range. This may be one of the only reasons you need to shoot for a specific pH.
How to Test Your Tap Water’s pH
Many hobbyists test their tap water right away for pH. However, this is not a good indication of your “true” pH. To properly measure your tap water’s pH, pour some tap water into a bucket and place an air stone in the bucket to agitate the surface (to oxygenate the water). Then let this bucket of water sit out for 24 hours. After this, test the water for its pH. It is then a good idea to check it after 48 hours to see if there is any additional change. These values measured after 24-48 hours are an accurate measure of the “true” pH of your tap water.
So, why do you have to leave the water out for 24-48 hours? Carbon dioxide in the water causes the pH to drop. By exposing your tap water to the air and agitating the surface, you are causing a gas exchange at the surface of the water (oxygen goes from the air to the water while carbon dioxide goes from the water to the air). This exchange reduces the amount of carbon dioxide in your water and causes the pH to rise. This pH will be the actual one you will measure in your tank (assuming there are no other objects/chemicals in the tank impacting the pH) as the oxygen/carbon dioxide exchange occurs in your aquarium constantly.
If you find that there is a major difference between the pH of your water right out of the tap and the pH of your water after 24-48 hours, the easiest way to do water changes and not stress your fish is to buy a bucket or two, fill them up with water, add an airstone to each, and let the water sit out for 24-48 hours. The pH will then be adjusted to its actual value and you can use the water for your water change.
How pH Impacts Other Compounds
Your pH impacts other aspects of your water chemistry. For instance, if your pH drops below 6, the nitrification bacteria that keep your ammonia and nitrites (toxic compounds to fish) at zero ppm, will begin to die off. This can cause your tank to re-cycle and kill you fish in the process if they are not hardy enough.
The toxicity of ammonia is also largely dictated by your pH. The total ammonia in your tank is a combination of ammonium ions (NH4+) and ammonia (NH3). The pH of your water is the major factor in the relative concentrations of these two compounds. More ammonia (the more toxic of the two compounds) will be present in alkaline water while more ammonium ions (the less toxic of the two compounds) will be present in acidic water. Therefore, you need to remember that as you raise the pH, you are making the any ammonia in the tank more toxic to your fish. It is because of this that pH adjustments during the cycling phase of your aquarium are not recommended. After the cycle is completed, there should not be any ammonia in your tank anyways.
The Relationship Between pH and kH
kH is a measurement of the carbonate hardness of your water. In other words, it measures the concentration of carbonate and bicarbonate ions in your aquarium. kH also indicates your water’s buffering capacity – your water’s ability to neutralize added acids without significantly changing the pH. Therefore, a higher kH corresponds to a more stable pH in your aquarium and a lower kH can correspond to large swings in the pH. Generally, if your kH is below 4.5 odH, you need to closely monitor your pH for large changes. You will also need to be more consistent in your water changes as the low kH will cause the pH in your aquarium to consistently drop with time. Frequent water changes are the best way to keep the pH up to an appropriate level.
Check Your Test Kit
I have seen numerous examples of test kit measurements giving an incorrect reading. This can be especially frustrating as it may cause you to think there is a pH problem when there actually is not. Therefore, if you are getting a reading that is either too low or too high for your taste, the first step is to investigate your measurement methodology.
Most test kits have a shelf life (usually 6 months). If your test kit is older than this, it may be providing inaccurate results. Also, be sure to follow the directions exactly. I have heard of people shaking a bottle for 30 seconds instead of a minute and this causing an error in the test. Follow the test exactly as it was written. If you are sure the kit is not out of date and that you followed the directions exactly then you can be confident that you are obtaining an accurate reading of the pH.
Ways to Raise Your pH
As stated above, it is generally a better idea to acclimate your fish to the pH of your water than to adjust your water to suit the pH preference of your fish. However, some people still like to match the natural environment as close as possible or have a pH that is way outside the range that is acceptable to their specific species. If this is the case, there are several methods you can use to raise your pH.
● Water Changes – Over time, the pH in your aquarium will drop. The most effective method to raise it back up to the level of your tap water is to simply perform regular water changes. If you do not regularly do water changes, you may need to do several smaller ones (each separated by 24 hours) so that you do not shock the fish by making them go from a low pH to a high one immediately.
Vacuuming all of the uneaten food and waste will also help to counter the tendency for the pH to drop over time.
● Rocks or substrate - Add some rock work or substrate to the aquarium that has the effect of raising the pH. For example, crushed coral is used as the substrate in many African cichlid tanks (African cichlids prefer a high pH). Limestone and petrified coral will also do the trick. If you do not want to add these rocks to your aquascaping, you can add a bag of crushed coral to your filter or hide some of these rocks behind the rocks you do want to showcase. For example, I have an African cichlid tank that uses lace rock for the caves and I hide petrified coral pieces behind my rock wall.
Read the article on the site entitled Adding Rocks and Wood to Your Freshwater Aquarium for more information on which rocks will raise your pH.
● Aeration – Increasing the oxygen concentration in your water will serve to drive down the carbon dioxide concentration. As discussed above, less carbon dioxide translates to a higher pH. Therefore, you can increase the aeration in the tank to raise the pH. To read about aerating your aquarium, reference the article entitled Properly Aerating your Aquarium in the article section of this website.
● Baking soda – Adding baking soda will raise the pH, but remember that this will need to be constantly added (you cannot just add it once and forget about it). You also need to be careful not to add too much at one time and cause a severe spike as this could kill your fish. It is best to gradually adjust the pH if you decide it must be adjusted. A general rule is 1 teaspoon per 5 gallons. Dissolve the baking soda in some water before adding it to the tank. Also remember that the above ratio of 1 teaspoon per 5 gallons is just a rule of thumb. For your specific case, take it slowly so you do not shock or kill your fish.
● Shells – Adding shells to your aquarium will raise the pH.
● Removing Anything that May be Lowering the pH – Below is a list of ways to lower the pH in your aquarium. Study this list to see if you are accidently using any of these methods and getting a low pH as a result. For example, maybe you placed a piece of drift wood in your tank without realizing it would lower the pH. If this is causing you problems, remove the drift wood.
● Chemicals – There are several commercial buffers currently available on the market. However, these are generally not recommended as they can lead to large spikes in your pH and usually only serve as a temporary fix. They will not in general, maintain the pH in your aquarium. However, if you have tried everything else and nothing is working, the buffers may do the trick.
Ways to Lower Your pH
Lowering the pH is often more difficult than raising it. There are some methods you can try though.
● Filter Through Peat Moss – Filtering through peat moss is the most effective way to lower your pH. Some people also use peat moss in their substrate for the same effect.
● Add Carbon Dioxide – As we have talked about multiple times, increasing the carbon dioxide in your tank lowers the pH. Therefore, pumping in more carbon dioxide would result in a lower pH.
● Add Wood – Many types of driftwoods will lower the pH. To read more about using wood in your aquarium read the article on this site entitled Adding Rocks and Wood to Your Freshwater Aquarium.
● Chemicals – There are many products on the market today that will lower your pH. However, just like the chemicals that raise the pH, these pH lowering compounds do not maintain a stable pH.
It is much more important to have a stable pH than to have a specific value for your pH. Adjusting the pH in your aquarium can be dangerous to the fish as swings of just 0.3 in a day can be deadly. Therefore, unless you have a specific reason for doing so, it is better to acclimate the fish to your tap water’s pH than to adjust your pH to fit the preference of your fish.
For additional information, refer to the following web pages:
Most Recent Articles:
Aquatic Mosses for Freshwater Tanks
If you like the idea of a planted tank but aren't ready to take on the extra work load, start off small with some aquatic mosses.
Wavemakers for Saltwater Tanks
If you want to keep your saltwater tank healthy, you need to consider the ideal level of water flow. Installing a wavemaker in your tank will help you strike the right balance.
Choosing the Correct Temperature for a Marine Aquarium
One of the most important things you must to do ensure the health of your marine tank is to achieve and maintain the ideal temperature.
- More articles: General Aquarium Articles, Freshwater Aquarium Articles, Saltwater Aquarium Articles, Product Reviews (Freshwater), Product Review (Saltwater)