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4.4.2. Buffering the Water

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Author : David Bogert

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Time To Read :
5 minutes
Difficulty : Level 7

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Buffering makes water resistant to changes in pH but it is rarely needed in any aquarium.
Simply put buffering is the ability of water to resist changes in pH. Many people comment about the importance of a stable pH and having a buffered system. The importance of pH is vastly overrated as aquarium product suppliers want to sell the unsuspecting newcomer a bunch of “pH Up”, “pH Down”, “Malawi Buffer” or “6.5 pH” products. It is just not important.

This is examined in more detail in this link:

4.4.1. pH is not Important

A high carbonate content (i.e. a high KH) buffers the water and prevents something called a “crash”, so many key in on KH. But “crashes”, where the pH becomes very low, only occur in very poorly maintained tanks or new tanks where the water is rarely or never changed. It is something called “Old Tank Syndrome” and is rarely encountered. During intensive cycling with a lot of ammonia it becomes necessary to add a carbonate or a bicarbonate to keep the pH above 7.0 with a KH over 1.

picture of an aquarium fish threadfin rainbow fish
threadfin rainbow fish

Buffering the pH up with Acidic Waters

One very easy way to make soft or acidic water fine for any fish is to use a bag of crushed coral, aragonite sand or crushed shells in the filter. This buffers to an excellent 7.6 to 7.9 pH. This is an excellent pH even for Amazon fish. But note that the “7.6 to 7.9” is an average. At times an aquarium with crushed coral can be 6.9 pH and at times it can be 8.5 pH. This is because of variations in dissolved carbon dioxide which occur naturally in any aquarium.

Crushed coral and aragonite take days or even weeks to work. If they are placed in an area of high flow like inside a filter they will work much better. If they are placed in a bag in a corner of the aquarium where there is no flow they might takes many months to work.

And crushed coral will typically but not always only last three to six months before it becomes coated in highly insoluble phosphates. It typically needs to be replaced every few months.

Baking soda will also raise the pH. Baking soda CAN, in sufficient quantities, raise the pH higher than crushed coral, all the way up to the 8.5 pH range. Note that baking soda also takes time to work. So adding baking soda should be done slowly. Add some baking soda to the aquarium and wait two days. If you are above 7.5 stop. If you are below 7.5 add more and wait four days.

Pterophyllum scalare Gold Longfin Angelfish
Pterophyllum scalare – Gold Longfin Angelfish

Alternatively, a commercial aquarium buffering agent can be used if you like burning money. All commercial high pH buffering agents are simply baking soda and a small amount of other salts with a very high price tag.

Note that carbon dioxide, carbonate hardness (KH) and pH are interrelated in very convoluted and complex chemical pathways. This is the “Bermuda triangle” of the aquarium chemistry. Go there and you may never come out. I’m a chemist and I don’t try to control this triangle. Just keep the pH between 6.5 and 8.5 and total dissolved solids above 60 ppm and ignore the rest. The topic is covered in some depth in this link:

4.5. Water Hardness

Buccochromis heterotoenia
Buccochromis heterotoenia

Buffering to a Lower pH

For buffering lower pH one can use commercial buffering chemicals available in aquarium suppliers web pages. I don’t recommend commercial 6.5 or 7.0 buffers because they are all phosphates, and phosphates will give you huge problems with algae growth. Also if you have water with any degree of KH (over 4 degrees), acid buffers just won’t work.

Seachem sells some acid “buffers” which don’t have phosphates in them. These are sulfites and other sulfurous acid compounds. They do  bring down the pH just like pool acid will bring down pH but they DO NOT buffer. 

Buffers by definition hold a pH at a set value against the addition of either bases or acids. Seachem low pH “buffers” don’t do that, they only lower pH. They do NOT buffer, they are simply acids. There is a BIG difference. Sulfurous compounds buffer in the range of 4 to 5 pH, not in the range of 6 to 7 pH.

This means it is very easy for an aquarium “buffered” with the Seachem “buffer” to drop to 5.5 pH which could stall the cycle completely (and make nitrite quite poisonous). This is not desirable. One shouldn’t use Seachem low and neutral “non-phosphate” buffers simply because they are NOT buffers. 

picture of an aquarium fish Trichogaster lalius Dwarf Gourami
Trichogaster lalius – Dwarf Gourami

pH in Depth

For those interested in a more in depth discussion of pH click on the following links:

Link to general discussion of pH:

4.4. Aquarium pH

Link to a more in depth discussion of pH and how unimportant it is in the aquarium:

4.4.1. pH is not Important

pH goes up and down constantly in an aquarium because of carbon dioxide and how it interacts with water. This is another relatively complex topic:

4.4.3. Carbon Dioxide and pH

There are situations when one has a pH greater than 8.5 and one needs to drop the pH. This link covers how to safely drop the pH of water

4.4.4. Dropping pH

And sometimes water out of the faucet that has set for two days has a pH less than 6.5 or 7.0 and needs to be raised. This link covers how to safely raise the pH:

4.4.5. Raising pH

Many people think that fish which have been bred in a wide range of waters can thus tolerate a wide range of water. This is simply a myth.

4.7. Fish Tolerance to pH

And many think that fish must be kept in a very stable pH or temperature and that rapid changes are detrimental to the fish. This is yet another myth.

4.8. Stability Isn’t Important

Copadichromis chrysonotus White Blaze
Copadichromis chrysonotus – White Blaze