VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

TOO LOW (TOO ACIDIC) pH

• Fish species differ in their optimal pH. A pH range of 6.5 - 9.0 is generally recommended for freshwater fish. Marine aquarium requires a stable, alkaline pH. The tolerable pH for marine aquaria is generally 7.8 - 8.4. Optimal limits are much narrower and the pH is best kept between 8.1 and 8.3. Fish acclimated to relatively low pH survive a drop in pH better than the same species maintained at a higher pH.

Sources of low pH water

• Most ground water has dissolved carbonates and carbon dioxide and a pH between 5 and 8. Ground water in contact with silicate minerals is poorly buffered and typically has a low pH and a large amount of CO₂ compared to ground water taken from carbonate substrate that is thus well buffered. In ponds, pH is highly influenced by the soil type.
• The metabolic activity of fish and other aquatic organisms produces acids. In a closed system such as an aquarium or ponds, these acids tend to gradually reduce pH. A pH below 5.5 is very stressful, if too low, it is lethal. Acute exposure of fish to such a low pH can be fatal.

Clinical signs of low pH

• Acute mortality with tremors and hyperactivity, dyspnea and acute stress response. Chronically low pH leads to increased mucus production and chronic stress response.

Diagnosis of too low pH

• A good colorimetric test is adequate for routine clinical measurements of pH. But low- cost, portable pH meters are more convenient. The toxicity of low pH is also complicated by its influence on so many water quality variables especially ammonia and other toxins. Low pH stimulates increased mucus production. This interferes with gas and ion exchange.

Treatment of too low pH

• Aquaria: Change water, add buffer, adjust pH only if ammonia levels are safe
• Ponds: Add buffer, reduce the density of fishes
• Flow - through system: Pretreat incoming water with buffer or add base