Keeping the pH of saltwater aquariums in check

ph water measurement

Most saltwater aquarium owners are always concerned about the pH level. While fish-only systems may take a broad variety of pH levels for short periods of time without injury, reef tanks, which include both fish and invertebrates, need substantially on a continuous pH level in the appropriate range merely to exist, much alone thrive. A basic saltwater system's pH should be between 7.6 and 8.4, however reef tanks are more sensitive and should be managed at the higher end of the pH range, between 8.0 and 8.4.

To control or adjust pH, one must first understand what it is. Although understanding the chemistry of how ions interact can be complicated, developing a layman's understanding of pH is not hard.

A Basic Explanation of pH

The pH (potential hydrogen) of every solution is simply a measurement of its acidity or alkalinity. A pH of 7 is "neutral," meaning it is neither acidic nor alkaline, whereas a pH of 7 is alkaline or "base," and a pH of 7 is acidic.

The usual tendency for water in a saltwater system is for the pH to drop, or become more acidic, when acids are added to the aquarium. These acids come from a variety of places, the most common of which are:

  • Excess carbon dioxide (CO2) from respiration caused by lack of sufficient gas exchange
  • Nitric acid from biological filtration (nitrification)
  • Organic acids from metabolic wastes

Respiration and metabolic waste are, of course, a natural feature of the ocean. The pH of saltwater, on the other hand, does not vary because it includes a variety of substances such as bicarbonate, calcium, carbonate, borate, and hydroxide, which all function as natural "buffers" that prevent the pH from dropping.

So, how does alkalinity factor into this? The "alkalinity" of a solution is defined as the degree to which it retains its pH when acid is introduced. Carbonate or calcium hardness, and its German counterpart, KH or dKH, are related concepts used in aquariums. Alkalinity is determined by the number of "buffers" in seawater.

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

Ways to Remedy pH Problems

  • To raise pH, easy methods are to add bicarbonate of soda (baking soda), or a commercial pH adjustment product.
  • To lower a high pH, quick-fix remedies are to add some vinegar or lemon juice, or a commercial pH reduction product.
  • For stabilizing pH, the generally accepted "tried and true" method 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.
  • Installing a calcium reactor, although a more expensive option, can provide a no-hassle solution to control radical pH and alkalinity problems.

Keep in mind that any significant changes to the pH level in your tank should be made gradually. pH shock can kill practically any saltwater fish (and invertebrates) if the pH is raised from 7.4 to 8.4 in a couple of minutes. If you're making significant changes, go cautiously, just as you would when acclimating newcomers to your tank.

Preventing pH Problems

Without other effects, saltwater will retain a constant pH. Why, therefore, does the pH in your saltwater tank fluctuate, frequently becoming lower? The acid created by the generation and reduction of ammonia is the most common cause of a pH decrease. The cattle in the tank produce ammonia as they eat food and produce waste (mainly detritus) that decomposes. As uneaten food decomposes at the bottom of the tank, ammonia is produced. The same may be said for any deceased creatures left in the tank.

Regular tank care, including the removal of fish waste and uneaten food, as well as partial water changes with new saltwater, will generally keep the pH in your aquarium at the right level, eliminating the need for pH adjustments.

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