Some water gardeners refer to an algal bloom as pea soup, because of the green, opaque appearance the water takes on. Sometimes the water will appear to be tea colored or have stringy algae in it. Any manifestation of an algal bloom is irritating but most of the time unavoidable.


But Why?

Without going into too much scientific jargon including phosphates, biomasses, and oxygenation levels, ponders encounter algal blooms from time to time for some very specific reasons:

*The Yearly Cycle

Especially in cooler climates, where ponds go dormant during winter, the pond will go through a yearly cycle as it wakes back up in the spring. Bacteria go dormant with the fish and plants during the winter, and unfortunately algae, just like a garden weed, takes advantage of this. As the pond ecosystem comes out of dormancy, algae can take over before the beneficial bacteria and desirable plants have a chance to reestablish.

*The Over Under

Three sure fire ways to create an unhealthy situation in your pond are under filtering, overstocking, and over feeding.

  • Underfiltering: Your filter and pump should be turning over the volume of your pond at least once per hour. For example, if you have a 700 gallon pond, you should be using a 700 or more gph (gallon per hour) pump. You should also be using some kind of biofiltration which can include Bioballs, lava rocks, surface plants, or a bog with plants. Any place where beneficial bacteria can colonize will suffice as a biological extension of your filter.

If your water is not being filtered adequately, you will surely have problems with algae and clarity.

  • Overstocking: While very tempting to water gardeners, over stocking might be one of the most dangerous things to do in a pond environment. Overstocking fish, especially "dirty" fish like goldfish, can create an excess of bad bacteria in the pond. The excess nutrients (fish waste) will supply endless fodder for your algae problem. Fish should be stocked at 1" of adult fish per 10 to 20 gallons.

  • Overfeeding: Over feeding your fish is a problem that is based on the same principle as overstocking; it creates an overabundance of nutrients in the pond. If fish food has a chance to sit in the pond for long periods of time, the extra nutrients will feed the algae and not your fish. Fish should be fed only as much as they will eat within three to five minutes. Any extra food should be skimmed out with a net after said amount of time.

*Sun vs. Shade

The concept of sun versus shade in the pond environment sometimes seems a little backwards. You need to provide shade to the depths of your pond to keep the available sunlight at a minimum for algae. Algae will help itself to all the sun you give it, growing unchecked until something out-competes it for sunlight. This in another reason why algae blooms happen at the beginning of the pond season: there are no surface plants to shade the water. The more water lily pads and floating plants such as water lettuce and parrot's feather the better because they will take the sun's energy before it gets to the algae.

Variations in temperature and weather can also affect algae growth in your pond. Heavy rain and temperature fluctuations can disrupt the natural cycle of your pond resulting in algal blooms.

What can you do?

If you understand the above reasons and have corrected all that you can in order to lower the nutrients available to algae and your still have problems, there is some things you can do. Some are natural, some chemical, so you need to decide which path you want to take. It is advisable to start with natural treatments so you don't disrupt the ecosystem in your pond, though sometimes chemicals are necessary to correct the problem.

*Natural Methods:

Water Changes - The cheapest and first method you should attempt when trying to achieve clear water is water changes. Remove up to 20% of the pond water at a time and replace it with clean, clear tap water. Be sure to check and treat chlorine levels if you replace more than 20% at a time. You can use this method twice a week for as long as it takes to get on top of your algae problem.

Barley - Barley acts as a natural filter and preventative for excess algae particulates in water. You can use barley bales or pads, which are literally chunks of dried natural barley hay; or you can use barley extract which purportedly serves the same function. It is also said that barley produces a compound that inhibits new algae growth when introduced into the pond environment. Barley is readily available at pet and pond stores.

Beneficial Additions - Adding beneficial elements to your pond such as enzymes, microbes, and bacteria can help the system establish and clean itself faster than without.

EM - 1 : A liquid concentrate of microbial agents helps to naturally and quickly clear the pond and keep it clean. While it is expensive, first hand experience from ponders shows that it works.

Microbelift: Microbelift is a liquid beneficial bacteria supplement for the pond which helps break down algae and promote healthy nitrite and ammonia levels.

Other products to look at for natural pond clarification: Bio- Pond Tabs, GreenEx, Simply Clear, and EcoFix.

*Non-natural Methods:

Be aware that as you add non-natural ingredients to your pond you may be disrupting the healthy ecosystem in your pond.

Pond Clarifiers - There are many pond clarifiers out there that will successfully and quickly clear your pond water. Products such as AccuClear and CrystalClear products work rapidly as flocculants to clarify water. Flocculation refers to the clumping together of particles which allows for your filter to easily process them out of the water.

Algaecides - Algaecides such as GreenClean and Algaefix, chemically work to kill all kinds of algae that you might be having problem with. They are safe for fish and plants and work rapidly to clear ponds of algae.

Don't feel bad, algal blooms even happen on a large scale. It's just part of the natural process! Check out this satellite image captured in 1998 of an algal bloom in the Bering Sea.


Algal blooms can happen to anyone with a pond at any time. Hopefully you are keeping your pond in good health and can minimize algae's impact, but in case you have a bloom this summer use these tips to stay ahead of the pea soup. Here's to clear water!


Thumbnail and 'clear' water picture belong to Susanne Talbert, others were found on WikiCommons and are free use.