Algae is a normal part of a healthy pond, so the goal is not to remove every bit of it. The goal is to keep it in balance. Before treating algae, first decide whether you have string algae or green water, because each type responds to different solutions.
First Step: Identify the type of algae
String algae
String algae is the green, hair-like or filamentous algae that attaches to rocks, plants, waterfalls, and stream areas. A light amount is normal. In moderation, it can absorb excess nutrients and help support a balanced ecosystem.
Green water
Green water is caused by suspended, single-celled algae. It reproduces quickly and turns pond water green and cloudy.
If you have string algae
A small amount of string algae is not necessarily a problem. Koi often graze on string algae, and a bit of algae in the pond can be part of a healthy, active ecosystem. The goal is usually to control heavy growth, not completely eliminate every strand.
What works for string algae
- Remove heavy clumps by hand, with a brush, or with a pond net. Manual removal improves appearance right away and helps lower the nutrient load feeding additional algae growth.
- Add beneficial bacteria to help break down fish waste, leaves, uneaten food, and other organics that feed algae.
- Spot-treat algae on waterfalls, fountains, and rocks with EcoBlast™ Contact Granular Algaecide (US only).
- For ongoing filamentous algae, use the IonGen® System G2. It is designed for string algae and can be used in ponds with fish and plants when copper is monitored carefully.
If you use IonGen, remove as much algae and debris as possible first, keep the probe in an area with good water flow, and clean any scale off the probe if it builds up. Copper should stay below 0.25 ppm (0.25 mg/L), and alkalinity should be kept between 100 and 250 ppm (100–250 mg/L) for best performance. Results may take several days to a few weeks, and you may not see clumps of string algae dying back for about 2 to 3 weeks.
If you have green water
Green water is a suspended algae problem, so products meant for attached string algae will not solve it. What works best is UV clarification and filtration.
What works for green water
- Use an UltraKlear® UV Clarifier or UltraKlean™ Pond Filter, to eliminate single-celled algae as water passes through the ultraviolet clarifier.
- If you are using the UltraKlean™ Pond Filter, set the UV timer to 24 hours during an active green water bloom. After the water clears, reduce the setting to 12 hours on / 12 hours off or 6 hours on / 18 hours off.
- Backwash the UltraKlean filter about every two weeks, or sooner if flow slows, and backwash for about 1 to 3 minutes or until the water runs clear.
- Replace the UV bulb after 12 months of continuous use on the 24-hour setting for best clarification. The timer feature can extend bulb life to about 2 years on the 12-hour setting or 4 years on the 6-hour setting.
Help keep algae from coming back
Long-term algae control is about reducing excess nutrients and improving overall balance in the pond. Too much sunlight, overfeeding, excess fish waste, poor filtration, and outside nutrient sources such as runoff can all contribute to algae growth. Aquatic plants, shade, regular debris removal, and strong filtration all help keep algae under control.
Quick rule of thumb
- String algae = remove the excess, support the ecosystem, and use string-algae treatments when needed.
- Green water = use UV clarification and proper filtration.