Properly Maintaining the pH in a Freshwater Aquarium
Updated January 22, 2014
Written by Katherine Barrington
Learn how about pH and how to properly maintain it in a freshwater aquarium.
When it comes to maintaining water quality in your freshwater aquarium, pH is a significant factor. The pH of your tap water may not be ideal for the type of fish in your tank, so you need to learn how to test the pH and alter it, if necessary. 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.
The Basics of pH
The pH of water is measured on a scale that ranges from 0 to 14. A pH level of 7.0 is said to be neutral while values below 7.0 are acidic and values above 7.0 are alkaline. The pH level of a body water varies according to a variety of factors including chemical concentration, the present of trace minerals, even the type of substrate. This being the case, different species of fish are adapted to different pH levels – the level that works for one fish might not work for another species of fish. This is why it is incredibly important that you do some research before you add any fish to your tank – you need to be sure that you know what pH levels they require and that the different species in your tank are compatible in this way. If you do not provide your fish with the right pH level, they may become stressed and could fall ill as a result.
By Piercetheorganist at en.wikipedia [Public domain], from Wikimedia Commons
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.
How pH Impacts Other Compounds
The pH of your tank water has an impact on several aspects of water quality and water chemistry. For instance, if your pH drops below 6.0, 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 your 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 (pH above 7.0) while more ammonium ions (the less toxic of the two compounds) will be present in acidic water (pH below 7.0). 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
A kH level 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
The best way to keep track of the pH in your aquarium is to purchase and use an aquarium test kit. You can buy these test kits at your local pet store or order them online. Test kits come in several different forms – one uses a test solution to change the color of a water sample based on the characteristic being tested. A second type of test kit involves dipping a strip of test paper into a water sample and then comparing the color to a chart included with the kit. Unfortunately, it is easy to misuse a test kit and to get 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.
By Flickr user Cybergibbons
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. As another back-up method, you can also take a sample of your tank water to your local pet store to have it tested (often for free).
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 the pH level in your tank.
● 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 rather than one large one (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. Be very careful when using this method, however, because it could raise the pH in your tank beyond the appropriate level.
● 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 in a freshwater aquarium 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.
Though your aquarium fish may prefer a particularly pH in their native environment, 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.
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