Acidity (pH) (part 2)

In In part 1, we stated that pond fish, and cyprinids in particular, thrive best at a stable pH between 7 and 8. Pond fish do not tolerate pH that is too low, too high, or fluctuating significantly.

pH too low

A pH that is too low causes part of the biological filter to lose its effectiveness. The nitrifying bacteria that break down ammonia and nitrite are less efficient at a low pH. Fish can develop mucous membranes damaged by the acid, and soft tissues such as fins can also die. The fish will often jump to escape their habitat.

Pond water can become “acidic” (pH drop) because hydrogen (H+) is released during the nitrification process , if the KH is almost depleted. In addition, large amounts of CO2 can lower the pH. You'll need to replace the water sufficiently to maintain the KH and provide sufficient aeration to flush out the excess CO2 from your system.

pH too high

At too high a pH the balance shifts Ammonium to ammonia . This can lead to poisoning at high ammonia levels. Fish can develop lye disease. To defend against the alkaline water, the fish will first produce extra mucus. This exhausts the goblet cells that produce the mucus, causing the fish to lose its entire mucus membrane under the influence of the alkaline environment and become rough to the touch. This paves the way for external parasitic attacks. The gills can also be affected. The fish will often jump to escape its habitat.

Factors that can raise the pH include materials containing lime, such as some substrates and cement. Furthermore, excessive aeration can cause the pH to become too high, leading to a CO2 deficiency in the water, which in turn raises the pH. Properly adjusted aeration and avoiding lime-containing materials prevent excessively high pH.

pH fluctuates

A sharply fluctuating pH is often seen in ponds with a lot of algae and/or underwater plants. Green plants use carbon dioxide (CO2) during the day and produce oxygen (O2). At night, this is reversed, with O2 being used and CO2 being produced by the same plants. This can lead to a CO2 surplus at night. This lowers the pH because there is a direct relationship between pH and CO2. It appears that with an increase in CO2, the pH drops and vice versa. In the morning, you'll measure a lower pH than in the evening. If there's a difference of more than 0.3 pH points, the fish will feel uncomfortable. They have to constantly adapt to the changing pH. This causes stress, which weakens their immune system and makes them more susceptible to disease. In such a case, by aerating at night and not during the day (the plants will still produce sufficient O2, so you don't have to worry about oxygen deficiency), you can neutralize the fluctuation.