How to Eliminate String Algae (Debris) in your Pond

At some point during owning a pond, you have likely encountered string algae – also known as filamentous algae, blanket weed, hair algae or just pond debris or pond scum. String Algae is a common pond pest that can multiply quickly in the right atmosphere (warm water and plenty of nutrients).

In This Article We Will Discover

  1. What is string algae?
  2. How to quickly eliminate string algae
  3. How to naturally reduce string algae
  4. How to prevent string algae

What is String Algae? This is a type of algae that attached itself to rocks, liner and waterfalls. This algae takes on the appearance of string or hair like filaments and, if left untreated, can grow to long lengths within a pond. Sometimes, this algae will hold bubbles within its fibers and float to the surface of the pond, appearing more like a blanket weed. The best way to distinguish between the two main forms of algae in your pond - suspended algae (green water) and filamentous algae, is the following: you will be able to physically pick up filamentous algae or pull at it – whereas, suspended algae is simply green water.

Quick Fix for String Algae

As quickly as string algae can show up in our pond is about a quickly as we would all like for it to disappear. Unfortunately, most methods to get rid of string algae in our ponds involve time and patience. There is a product we recommend for fast removal of string algae in your pond. This product is not generally used as a full time solution for most, but does wonders when you need a quick fix for your algae problem.

D-Solv Powder uses the power of oxygen to remove debris quickly from waterfalls, liners and the bottom of your pond

  • May be used in ponds containing fish and plants;
  • Application: Sprinkle around the edges of your pond and directly on your waterfall (where you see debris);
  • Should only be applied a maximum of once per week;
  • Application Rates (Surface area of pond):
    • 1 fl oz - Treats up to 25 sq ft;
    • 2 fl oz - Treats up to 50 sq ft;
    • 4 fl oz - Treats up to 100 sq ft;
    • 8 fl oz - Treats up to 200 sq ft;
  • Ensure there is vigorous aeration present when using this treatment;
  • Do not mix with other treatments.

What Causes String Algae to Form in your Pond?

We have heard many different scenarios regarding people’s experiences with string algae; some have had it in their ponds since day one, some have it early spring and have it slow down later in the year or some haven’t had it since they built their pond and all of a sudden it has emerged years later.

There is always a reason for algae forming in a pond. String algae is caused by either one or multiple reasons below:

  1. Increasing Temperature of Water – increased sunlight – the sun feeds all plant life including pesky string algae;
  2. Heavy Nutrients in the Water – This can happen from many sources – most often fish waste/too much fish food, plants and debris breaking down in the pond or runoff from surrounding areas that contain fertilizers/nutrients (common after heavy rainfall);
  3. Low Levels of Bacteria – Having low levels of beneficial bacteria will cause more swings in water quality as bacteria acts to keep a balanced cycle;
  4. Pond Chemistry - Increase in PH and Phosphorus will lead to algae blooms – this relates back to fertilizers entering your pond, cut grass entering your pond and high fish levels as the most common sources.

Is String Algae Bad for the Pond?

String Algae – though not a beautiful sight to most pond owners – it is not always a bad thing in a pond. Short string algae (generally under 3”) or light coatings within the pond, are actually healthy! Koi and Pond Fish also enjoy snacking on this nutritious algae. However, once string algae becomes overgrown it can become harmful to a pond environment by reducing oxygen levels, so be careful that it doesn’t get out of hand!

Solutions to Prevent and Remove String Algae from your Pond

Product Quick Overview What it Does/When to Use

D-Solv Powder

  • See results in: as little as a few hours;
  • Quick Fix;
  • Great for Streams and Waterfalls.

When to Use: Use D-Solv powder when you are looking for a quick fix for string algae. Works particularly well on streams and waterfalls.

Application: Use once a week maximum and stick to the recommended dosing rates. On waterfalls and streams – turn water off, sprinkle the powder over the affected area, wait 20 minutes before turning the water back on. For inside the pond, sprinkle around the edges of the pond.

How it works: D-Solv powder uses oxygen power to remove algae debris from waterfalls, streams, rocks and liner within the pond. Works great as a spot treatment too! Non-toxic to fish and plants (using the recommended dosing rates). One of the fastest algae removing treatments on the market that is fish and plant safe!

Beneficial Bacteria

  • See results in: 2-4 weeks – slow but steady;
  • Aids in all aspects of the pond;
  • All natural.

When to Use: It is recommended that you use beneficial bacteria once a week as a maintenance dose to keep a balanced pond environment. Beneficial Bacteria is particularly important when there are fish present in the pond. Long term solution.

Application: Follow directions on the bottle. Add once weekly. Works best when there is aeration present in the pond. Turn off UV sterilizer (if present) for 24-48 hours every time you add bacteria as free floating bacteria will be destroyed with UV.

How it works: Beneficial Bacteria is naturally present in ponds, however, when we add fish and feed those fish, our ponds cannot keep up with the load we have applied and this is why we boost our ponds with natural, beneficial bacteria. It also helps if you give this added bacteria plenty of surface area to adhere to by also adding extra media (bio balls, string media, filter media mats etc).


  • See results in: 1-4 weeks;
  • Aids in all aspects of the pond;
  • All natural – Non-toxic.

When to Use: Use Nualgi if you are looking for a long term solution to algae without the use of UV or Ionizers. Nualgi is great for fish and plant health. Non Toxic Product.

Application: 1 ml treats 1000gal! Treat early morning, once a week. Overdosing will not aid the pond. You will generally see results in 1-4 weeks. Works well with the use of beneficial bacteria and added aeration – no other products required.

How it works: Within 3-5 hours of applying Nualgi to your pond, a bloom of Diatom Algae (good algae!) will develop. This algae is not visible to the naked eye and out competes blue and green algae in the pond for nutrients, thus starving the blue and green algae allowing it to die off. The diatoms lock in the nutrients and are then consumed by your fish creating a full cycle that not only benefits your pond water but your fish and plants as well! (Diatoms are a free floating algae that sink to the bottom of your pond where they are eventually consumed by your fish) Nualgi allows you to clear up nuisance algae, feed your fish less and increase dissolved oxygen levels!


  • See results in: 6-8 weeks;
  • Use in early spring for best results.

When to Use: Use Barley Straw early in the season as the results take time. Good for long term maintenance. Slow release.

Application: Apply close to the surface of the pond where sunlight is available, oxygen must also be present for barley to work to the best of its ability. Best to use barley early spring – mid-summer (not as effective in fall) as it generally takes 6-8 weeks to see results.

How it works: Barley works by slowly breaking down, becoming active and forming hydrogen peroxide in small doses that effectively work to inhibit the growth of algae.

Increased Oxygen

  • Benefits all aspects of the pond;
  • Considered a must with ponds that contain fish and plants.

When to Use: Aeration should be utilized at all times in a pond. Increased oxygen levels are beneficial to water quality, fish and plants during spring, summer, fall and winter.

Application: Have your air stones approximately 2 feet from the surface of the pond in the winter months with freeze over to not disturb fish in dormancy. During spring summer and fall, air stones can be placed at the bottom of the pond for optimal dissolved oxygen levels.

How it works: The natural nitrogen cycle within a pond requires oxygen to cycle properly. Oxygen controls nitrogen and phosphorus levels, which in turn, controls algae spikes. Aeration will aid beneficial bacteria in decomposing debris within the pond. Having higher dissolved oxygen levels in your pond is required for not only healthy and clear pond water, but also for optimal fish health and plant health.

Ionizing System

  • See results in: 1-2 weeks;
  • Very effective;
  • Don’t have to get your hands dirty.

When to Use: Ionizers are a great choice for the pond owner that is looking to have minimal work when it comes to keeping a pond clean and clear. Ionizers are specifically for string algae and can be used at anytime during the season to eliminate string algae. This is a mechanism that allows for pond cleaning with little to no hands-on work.

Application: An ionizer is an easy install. It can be installed in-line with your hose with two easy connections or can hang in a skimmer where there is optimal water flow.

How it works: An ionizer slowly releases Copper Ions into your pond using a probe that sits within a chamber. There is a monitor that allows you to adjust how much copper is being released. Copper probes are generally replaced every 1-3 years depending on use. Copper, at small levels, effectively rids your pond of string algae. One must monitor copper levels to ensure that the level does not become too high as this may affect fish and plants.

Water Plants

  • See results in: 2+ weeks;
  • All natural;
  • Adds beauty to the pond.

When to Use: Water plants, when maintained, are always a good idea for a pond owner. In our warm seasons, plants compete with algae for nutrients in a pond and also help to shade the pond from increased sunlight.

Application: It is a good idea to use a variety of plants in a pond. Hardy lilies are great as they are low maintenance, survive year to year, and provided beautiful blooms throughout the summer. Floating plants like hyacinth and water lettuce are great for surface coverage, particularly in the spring before lilies have had a chance to take off. These floating plants also have large root systems and multiply throughout the season. Finally marginals, particularly when planted in a bog region of the pond, provide beauty to the edge of your pond as well as great filtration through their root system. These plants also return year to year which makes them a great investment.

How it works: Most water plants work in a multitude of ways to prevent string algae in a pond. First, many will provide shade (looking to cover approximately 50% of a full sun covered pond), shade will help prevent a surge of algae growth particularly in the high heat of summer. Second, their root systems compete with algae to take in nutrients from the pond, thus limiting algae growth. Finally they have the added benefit of playing a large role in the nitrogen cycle as they are required to consume nitrates that build up in the water.

Other Ways to Eliminate String Algae

  • Limit How Much you Feed your Fish - It is always a better option to feed your fish multiple times a day, smaller quantities of food, than once a day, a large quantity of food. Feeding small amounts at each feeding will prevent uneaten food and optimal fish health.
  • Remove any Uneaten Fish Food - Fish food that is left floating in the pond, uneaten by fish, is a huge nutrient source for algae. A quick way to limit this source is to net out uneaten food (anything that is not eaten after 5 minutes of feeding) as well as clearing out skimmer nets that may have captured floating food.
  • Feed Fish a Quality Food - Many people will underestimate the affect a cheap fish food will have on their pond and water quality. By feeding cheaper foods with fillers, fish will not retain much nutrient and their ill be heavy waste resulting from this lack of nutrient intake. By saving on fish food many pond owners will in fact pay much more to fix algae problems caused by low nutrient value in cheaper foods.
  • Physically Remove Long String Algae - Before applying a water treatment to aid in your string algae problem it is a good idea to physically remove long strands by pulling them out by hand. If there is a large die off of string algae in your pond, this can adversely affect your water conditions; also, water treatments will be more effective on small portions of string algae as opposed to large portions.
  • Avoid Large Water Changes – Stick to Small, Consistent Water Changes - Small water changes (10-15%) up to once every 1-2 weeks helps to renew specific minerals in your pond that deplete with time. Often homeowners will get frustrated with string algae – do a full pond cleanout – and are surprised to see more string algae return within a week’s time. When we do full or large water changes, we are essentially taking a mature pond with stores of beneficial bacteria and starting from scratch, which when it comes to ponds, bacteria levels are very important in controlling algae.
  • Avoid Leaching into your Pond-Particularly During Heavy Rainfall - Many homeowners are unaware of the fertilizers and debris that enter their ponds via the surrounding landscape. During heavy rainfall, lawn fertilizers and debris often leach into the pond, putting a heavy strain on the water quality. This is particularly common with natural ponds that sit lower than the natural grade of the surrounding landscape.
  • Don’t Overstock your Pond - Think of your pond like a city – cities that are overpopulated often have troubles with waste management due to lack of space – same goes for a pond. We often think ponds should be able to balance themselves like lakes – this would only be possible if our ponds were stocked like lakes. Instead, we add more fish than any lake would ever have and expect the pond to keep up. By adding heavier filtration or limiting the fish load in our ponds we can help prevent fish waste from adding to our algae issues.
  • Remove Debris like Leaves and Dying Plants - Again – it is all about not giving string algae additional nutrients and food to grow off of. Decaying plants and leaves put a huge strain on the nitrogen cycle and end up producing more nitrates and nutrients than our filters and ponds can keep up with. Our best option is to ensure our skimmers are working optimally to remove any surface debris and to net out or pull out any decaying plant life or material within the pond.