Restoring Rock Color in a Pondless Waterfall: Algae and Nutrient Control

Why Rocks Turn Black

Black coating = algae (likely cyanobacteria or diatoms) fueled by:

• High nitrogen/phosphorus (from tap water, soil, fertilizer, fish waste).
• Inadequate filtration.
• Excess light.

Remediation

1. Scrub rocks thoroughly.
2. Do a full water change.
3. Eliminate chemical fertilizers near the feature.
4. Add a proper biofilter (bog filter, waterfall filter).
5. Plant heavily in the stream (watercress, iris, pickerelweed) to uptake nutrients.

Inspiration: Swimming Ponds

European natural swimming ponds use plants and biofilm for crystal-clear water without chemicals. Higher upfront cost, near-zero maintenance.