How to Acidify the Water in Your Aquarium

The majority of freshwater aquariums, particularly community tanks, thrive at a neutral pH. If you are keeping a combination of fish with varying species and varying water requirements, your safest bet is to maintain a pH as close to 7, or neutral, as possible. Although almost all freshwater fish can survive at any pH between 6.5 and 8.5, some need more acidic water than average. To make your fish tank as viable as possible, maintain a pH balance in line with the needs of the species in your care.

Determine your target pH range by examining the needs of every fish in your tank. Ideally, you should have a biotope aquarium containing fish of similar or identical ecological backgrounds. For example, you have a "black water" biotope aquarium, which emulates the species an set-up of a tannin-rich, rainforested region of the Amazon, your water should be soft and slightly acidic, with a pH between 5.0 - 6.0. You should take measures to keep your pH within this range.

When to Acidify Your Water

To protect your fish, you need to acidify your aquarium any time that the pH exceeds the recommended range for the fish in your care. If you have a community tank and the pH nears or exceeds 7.5, or if your blackwater biotope aquarium rises above a pH of 6.5, you will need to promptly address the chemical problem to prevent injury or death of the fish in your care. The pH of your fish tank should remain relatively stable at all times, never fluctuating more than .1- .2 during any given week.

There is no way to tell the pH of an aquarium without testing it regularly. Most professional aquarists recommend that you test the pH of your aquarium using a litmus strip or similar testing device, available at your local pet supply store. Depending on how stable and established your fish tank is, you may need to test the pH as often as once per week, or as sparingly as one per month. Take measures to acidify your tank any time that your readings rise above your target range.

Natural Ways to Acidify Water

You can use natural ornaments and plant matter to acidify the water in your aquarium. In soft-water, acidic ecosystems such as those found in Amazon rainforest, the water is acidic because of the breakdown of peat, decomposing leaves and woods. This leads ot a high concentration of natural tannins in the water, and causes the classic "tea-stained" look associated with blackwater ecosystems.

You can add acidic tannins to your water naturally by adding unprocessed driftwood to your tank. Most fish supply stores sell rainforest wood appropriate for use in fish tanks. These products gradually release dark-colored, acidic tannins into the water, helping to raise the pH and give it a natural appearance. You can accomplish the same effect by adding a small amount of peat to your filtration system. Never add "wild" wood or peat to your tank unless you are very skilled and know exactly what you are collecting.

Commercial Products to Acidifiy Water

Several commercial products can help to acidify the water in your aquarium. One common solution is to purchase a water purifier which eliminates hard, alkaline minerals from your tap water. Perform a 50% water change with this purified water every three to four days until it reaches a stable pH similar to your target. Continue performing regular water changes with a purification system to prevent the alkalizing buildup of hard-water minerals.

Other commercial products, including the water additive "pH Down," contain weak acids designed to lower the pH of your aquarium. These can be reliable short-term solutions, but, as minerals in your aquarium buffer the acids, your water chemistry is likely to return to its original state. You may need to re-apply pH Down on a regular basis to prevent your aquarium's pH from spiking again. Test your water parameters regularly to assure that it is an appropriate environment for all the fish in your care.