September 25, 2016
What Does Black Spots on Your Pond’s Bottom Substrate Indicate?
If you see black spots on your pond’s bottom substrate layer, this indicates a low-oxygen environment caused by a high concentration of sulfur and/or amino acids. Another indication of this high concentration of sulfur and/or amino acids is a “rotten egg” smell.
Perhaps when you see/smell these indicators, it is time to consider employing a pond skimmer and/or biological filters, particularly those using Zeolite as the “active” ingredient.
But of course, before doing so, consult some pond dealers and/or specialty shops and do your “due diligence” too by reading about these skimmers and biological filters.