The pH of a body of water - its reading on the pH scale, which determines how acidic or basic the water is - is a critical component of maintaining the health of that body of water. Even the most minor of changes in the pH of a pond, for example, can have dramatic and long-lasting effects on the aquatic animal and plant life living in that pond. Knowing the ideal pH levels for ponds and measuring that pH regularly can go a long way in keeping your pond healthy and thriving.
Recommended pH
According to Texas A&M University's guide to managing pH in natural bodies of water, ponds should ideally fluctuate slightly from a lower to a higher pH throughout the day rather than staying at one static pH. A typical pond may start the day at a pH reading of 7.5 but increase to a pH of 8.5 or close to 9 as carbon dioxide is removed through photosynthesis. As aquatic plants add carbon dioxide back to the water through respiration, pH levels again fall at night. This slight pH fluctuation on a daily basis is one of the marks of a healthy pond.
High pH
Excessively high pH levels in ponds tend to be more problematic for aquatic plant and wildlife than low pH readings. Reducing a pond's pH levels can often be a time-consuming and complex process, since so many different chemical reactions can cause a pond's pH levels to spike. Adding gypsum, alum, some form of acid or another material to the pond can temporarily lower a pond's pH but will do nothing to address the underlying chemical reactions that caused the pH to rise in the first place. A more permanent solution to high pond pH is to adjust the aquatic plant life in the pond to reduce photosynthesis or to increase respiration so the net daily carbon dioxide uptake is near zero. Since carbon uptake and release by aquatic plants is the biggest determining factor for a pond's pH level, adjusting plant life in this way will greatly help to keep the water's pH consistently lower.
Ammonia Toxicity
Another major concern with high pH levels in a pond is ammonia toxicity. Ammonia is a nitrogen waste produced by aquatic plants and released into water; high pH levels convert ammonia to a more toxic form - un-ionized ammonia (NH3) - and low pH levels keep the ammonia in a less dangerous form - ionized ammonia (NH4+). Ammonia in its more toxic form can have deleterious effects on the plant and animal life that flourish in your pond, and these effects underscore the importance of regularly monitoring the pond's pH and taking measures to lower it when pH levels reach dangerous highs.
Monitoring and Managing pH
Water pH can be easily tested using an inexpensive water quality kit. Test the pH in the morning, in the afternoon and at night to observe the rising and falling pH cycle discussed in Section 1. There are many different materials and methods used to lower a pond's pH when it gets too high; sometimes a combination of several methods is needed to effectively lower a pond's pH over the long term. By monitoring your pond's pH and treating high-pH water as soon as you observe it, you can avoid the toxic effects of high-pH water on the plant and animal life in your pond.
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