Simple Remedies for Common Pond Algae

by Drs. Foster and Smith on October 6, 2010

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String algae at base of waterfall.

String algae at base of waterfall.

**Guest post from Heath S.**

There are two types of algae that thwart our ponds in Wisconsin:  Filamentous or “string” algae, and planktonic “pea soup” algae.  Over the years, I have combated both with sometimes-frustrated results.  It wasn’t until we had moved into our new home and had enough time for our pond to establish itself for a few years that the battle became a lot easier.

Let’s start with the planktonic form.  This type of algae multiplies fast and can prevent you from viewing your Koi.  The term “pea soup” is often used to describe a planktonic algae bloom.  In a natural pond setting, this type of algae is considered desirable because it is basically the beginning of the food chain.

When we provide food to fish in a containerized pond or epdm- lined pond, their food chain is interrupted, along with their natural grazing habits.  Therefore, the planktonic algae is no longer a necessary part of the diet of Koi and goldfish, thus it becomes an unsightly nuisance.

With no natural predators nor other plants to compete for the nutrients, this type of algae,  flourishes and rapidly reproduces causing the bloom.  Blooms can appear in many colors such as green, blue/green, brown or a variation between them.  Most often, I have encountered the brown color variety that has at times blocked the view of the fish until they surfaced for food.  I have mentioned before that I am not a fan of using chemical additives as a measure of defense, but I firmly believe in the use of AlgaeFix in correct dosage when extreme blooms are the case.

Water Iris, Cattail and Lily Pads are great nutrient consumers.

Water Iris, Cattail and Water Lilies are great nutrient consumers.

With my fish load, I have always had a struggle with filametous or string algae.  Normally it starts just below my waterfall and by mid-summer it is established throughout the pond.  Without using a chemical aide, the best defense in removing this type of algae is by hand and or the use of items such as the Algae Witch, a pole with a brush attached that you simply spin the algae around and remove from the pond.

I have never been overly concerned with filamentous string algae since it provides a food source for the fish as well as helps with the filtration of small particles.  Once out of hand though, it can cause a lot of work.  It will clog the prefilters, block skimmers, and choke out other plants such as water lilies.  It is not uncommon, with the right conditions, for this algae to grow a foot or more in a single day.

Preventing conditions that promote algae growth begins with a proper feeding regime.  Try not to feed more than your fish can consume in 5 minutes or so.  Immediately remove any uneaten food.  Test the water on a regular basis to ensure a balanced pond. Spikes in ammonia and phosphate, due to overfeeding, will fuel the growth.

Also provide plenty of shade by adding a variety of pond plants.  Water Hyacinth is a great plant for water cover and it spreads rapidly.  Up to 50 percent of the pond should have plant coverage.  I have included Hyacinths, Cattails, Water Iris, Water Lilies, and Water Mint in my waterfall filter.  This combination has proven successful for me.

As mentioned at the start of this post, your best defense is a pond that has had enough time to mature and establish a large enough bacterial base.  Each year gets easier than the last, enjoy!

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{ 2 comments… read them below or add one }

Bhaskar October 6, 2010 at 8:45 pm

Diatom Algae are the best solution to keep ponds clear of other algae.

Diatoms are very good food for Koi, so they are consumed by the fish and hence do not accumulate in the pond.

Filamentous Algae and ‘pea soup’ algae are the natural food for fish, that is the reason why they are not being consumed by the zooplankton and Koi.

Mike Moore June 24, 2014 at 7:15 pm

I have a pond and i love it. Been a couple really great summers with the same coys and goldfish. my pond is a small pond 500 gallon main pond with two 50 gallon waterfall tubs. I live in northern ky right south of cincinnati OH for some reason the algae is wearing me out this year. its at the point that im treating so much that im concerned for my fish! PLEASE HELP

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