One thing that may affect a pond in managing its algae and weed growth could be pH. What pH measures is the level of acidity or alkalinity that a body of water has. The closer to 0 your pH is, the more acidic it is. The closer to 7 your pH is, the more neutral the water is. Finally, the closer to 14 your pH is, the more alkaline or basic your water is.
The pH of a small garden pond can be critical to your fish and bacterial populations. Both of these groups need to have a pH in the 6 to 8 range in order for them to thrive. Unfortunately, algae and most weeds thrive in the same pH range. Therefore, it is futile to adjust the pH levels in order to eliminate algae and weeds, as this will also damage the natural aquatic life in the pond.
In larger ponds and lakes, pH is usually stabilized due to rain, run-off and the substrate (or bottom) materials that form the pond. The pH level may be affected by the use of acids, such as copper sulfate, but this would be such a minimal effect that the water’s pH would return to its normal range very rapidly as the algae, plants, and clay sediments take up the copper sulfate.
But one might want to know if pH can alter the effectiveness of algaecides and herbicides. Yes and no is the answer. Once again, if algae mats are present, then that would indicate that the pH is in a very effective range for these materials. This is because the algae and weeds only grow when the pH is suitable (usually between 6 and 8). Otherwise, the chemicals will not work when the pH is excessively low or high, but this is irrelevant.
Overall, pH should be considered mainly for the health of the pond, as it encourages the growth of beneficial bacteria
and other aquatic life. Measure your pH and strive to keep it within the range of 6 and 8.