One of your main goals as a pond builder should be to create a system that delivers top-notch water quality. In order to do this, it’s helpful to be familiar with principles of water chemistry needed to keep these systems in excellent shape.
Water chemistry is, as you may know, an enormous topic. Indeed, fully understanding and mastering its intricacies can be a lifetime pursuit. In the case of installing and maintaining natural water features, however, success can be achieved if you’re familiar with a few key constituents in water — including pH and nutrients — that support plant and animal life.
Most of us have heard of pH, but few pause long enough to learn what this common chemical term is all about. In essence, pH (which stands for “potential of hydrogen”) describes the relation of hydrogen ions to hydroxyl ions on a 14-point scale. In simple terms, the higher the hydrogen content and the lower the hydroxyl content, the more acidic the water. Conversely, the higher the hydroxyl content and the lower the hydrogen content, the more basic the water becomes.
On that scale, a pH of 7 is neutral. This means that the hydrogen and hydroxyl ions are in complete balance. Numbers higher than 7 are called basic (or, mistakenly, “alkaline” or “hard”), while numbers below 7 are termed acidic.
Typical ponds exist in a pH range from 6 to 11, which covers ground from the slightly acidic to the strongly basic. A pH of 8.2, for example, is highly acceptable for pond water, while a pH of 4 (which is acidic enough to dissolve nails) would be unacceptable if your aim is to sustain aquatic life.
Many factors influence the pH values found in water, with the presence of dissolved materials and metals being perhaps the most influential. These substances are commonly called buffers, and we typically talk about them in terms of alkalinity and hardness.
Alkalinity: When present at high levels, alkaline materials tend to hold the water’s pH at higher levels. The concentration of these buffers is expressed as parts per million (ppm).
Hardness: This is a specific form of alkalinity and refers to the amount of dissolved calcium, calcium carbonate and magnesium in the water. Water is termed “hard” when levels of these materials reach 300 ppm or higher.
When present at higher levels, these buffering factors tend to stabilize pH. In fact, when hardness and alkalinity values are high, it is less likely a pond will experience significant fluctuations in pH.
Beyond pH, there are other contributors to water quality that must be considered right up front, namely, the macronutrients and micronutrients that help sustain life in aquatic systems. In all, 17 of these essential ingredients — three macronutrients and 14 micronutrients — need to be included in ponds and streams.
The macronutrients are what we find in commercial fertilizer mixes. When you see a fertilizer that says 20-10-20, for example, these numbers refer to the percentage (by volume) of nitrogen (N), phosphorous (P), and potassium (K) in the mix. These are the nutrients required in the largest quantities for proper plant growth.
Nitrogen: In a pond, ammonia and nitrate are the most common forms of available nitrogen. High levels of either of those substances are good for plants (especially algae) but are toxic to most fish, so it’s best if they are undetectable or held at very low levels.
Phosphorus: Again, in a pond situation it is best to have low or non-existent levels of phosphorus, which appears in the water in the form of phosphates. Although in the case of a pond, these substances are not problematic for fish, they do invite prolific algae growth and therefore should be held at minimal levels.
Potassium: It’s rare to find high levels of potassium in pond ecosystems, but it wouldn’t be a problem in any event, because potassium is a key to both plant and fish metabolisms.
The other category you need to consider features the micronutrients. Fourteen of them are required for life: boron (B), carbon (C), calcium (Ca), chlorine (Cl), copper (Cu), iron (Fe), hydrogen (H), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), oxygen (O), sodium (Na), sulfur (S) and zinc (Z). Each is required in different ratios for different members of a pond-based ecosystem, and each plays a highly specialized role on the cellular level for all forms of life.