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Saltwater Aquarium pH Control For Dummies

Controlling Saltwater Aquarium pH and Alkalinity


The pH level in a saltwater aquarium is a constant concern to most aquarists. Whereas the occupants in a fish-only system can tolerate a fairly wide range of pH levels for periods of time with no major harm, the occupants of a reef tank rely heavily on a constant pH level in the right range to just survive, let alone thrive. The generally accepted pH level in a basic saltwater system is between 7.6 and 8.4, but reef tanks are a more sensitive, and therefore need to be kept at the higher end of the pH scale, 8.0 to 8.4.

To control or adjust pH, one must first understand what it is. In order to keep this discussion fairly basic, we won't get into the interactions of ions on a chemical level that make it all happen. Here we will just discuss what happens on a layman's level.

pH Simply Explained

pH (power of Hydrogen) is simply a measurement of the acidity or alkalinity of a solution. A pH of 7 is considered to be "neutral", neither acid or alkaline, while pH above 7 is alkaline or "base", and below 7 is acidic.

The normal trend for pH in a saltwater system is downward, or more acidic, which stems from the addition of acids into the aquarium. These acids come from several sources, the primary ones being: (1) excess carbon dioxide (CO2) from respiration caused by lack of sufficient gas exchange, (2) nitric acid from biological filtration (nitrification), and (3) organic acids from metabolic wastes.

Of course respiration and metabolic wastes are a natural part of the ocean, but the reason that sea water pH does not change is that the water contains a number of chemicals, such as bicarbonate, calcium, carbonate, borate and hydroxide, all of which act as natural "buffers" that retard the drop in pH.

So where does alkalinity come into all of this? The degree to which a solution maintains its pH when acid is added is termed the "alkalinity" of the solution. Related terms used in reference to aquariums are carbonate or calcium hardness, and its German equivalent, KH or dKH. The amount of "buffers" in sea water determines the alkalinity.

When the pH in a saltwater system starts to drop, it is an indication that the buffers are getting worn out, and the increase in acidity needs to be corrected.

Ways to Remedy pH Problems

  • Quick fix methods to raise pH are to add bicarbonate of soda (baking soda), or a commercial pH increaser product.

  • To lower a high pH, quick fix remedies are to add some vinegar or lemon juice, or a commercial pH reduction product.

  • The generally accepted "tried and true" method for stabilizing pH is still performing regular partial water changes. This not only refreshes the natural buffers, but also restores the trace minerals in the aquarium's water. Of course, reducing the causes of the drop in pH is always wise. Removing all uneaten foods and fish waste from the tank on a regular basis will go a long way toward retarding a drop in pH.

  • Use a simple doser to automatically add buffers as well as calcium, iodine, other essential trace elements and supplements.

  • Although more expensive, installing a calcium reactor can provide a no-hassle solution to control radical pH and alkalinity problems.

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