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Algae Bloom in Aquaponics System

When the aquaponics system is in the process of getting cycled, the population of algae often may go out of control resulting in an algae bloom.

Algae are common and natural in aquaponics system. In a balanced aquaponics system that is running smoothly, the algae population should be stabilized. When existing as a stable population, such as a very thin slime on the water surface or at the sides and bottom of the tank, algae is actually beneficial to the system as it is part of the ecology.

Dangers and Problems Caused by Algae Bloom

In the day: algae carry out photosynthesis, producing oxygen while consuming carbon dioxide and nutrients from the fish waste.

In the dark: Photosynthesis stops and the algae consume oxygen instead.

  • When there is an algae bloom in the fish tank, the dissolved oxygen and nutrient content of water in the fish tanks are depleted.
  • This effectively starving the aerobic organism in the aquaponics system (fish, aerobic bacteria and plants) of dissolved oxygen
  • This also depletes the nutrients needed by the plants.
  • When algae accumulate and die off, decomposition takes place. Decomposition is a process that consumes huge amounts of oxygen.
  • The changes in carbon dioxide levels (carbon dioxide is a weak acid) in the water during day and night as a result of photosynthesis by algae, can also cause swings in the pH levels.
  • Wild swings in pH levels can be very stressful to the health and well-being of the fish.

How do we combat the common algae problems?

Before you do anything crazy, follow best practices to prevent algae. These are easy and standard steps that you should be doing anyway!

  • Make sure temperature range is appropriate for the crops and fish.
  • Measure phosphorous to make sure that it’s not too high.

To reduce algae, there are several preventative and active measures you can take.


  • The simplest way to reduce algae is by shading because algae need sunlight to produce food, grow and reproduce.
  • The fish tank should be located in a shaded area and a cover should be placed at the top of the fish tank to block off as much sunlight as possible.
  • Moreover, a darker and cooler environment is preferred by the fish.
  • Pump full to aerate the system, bump up and clean your filters.
  • And very importantly, stop feeding the fish as all the nutrients will be going to the algae promoting further algae bloom

Mechanical filtration

  • In many systems, mechanical filtration plays a big role in algae removal.
  • Oftentimes this equipment is very expensive, but it can sometimes be made inexpensively. This type of equipment includes filters, screens, vortex and centrifugal settlement equipment, settlement tanks and other mechanical means of removing algae from the solution.
  • The media-based grow bed functions as a bio-filter. You may add some composting worms to the grow bed to consume the algae and uneaten dead organic matters.

Other techniques:

  • There are many other techniques, including the use of Ultra Violet clarifiers, barley straw, etc., but one of inexpensive techniques is the use of humic acid to “darken” your system water.
  • In very shallow water, adding humic acid to a system can actually stimulate algal growth, but in deeper waters, the use of humic acid darkens the water and shades out the depths of the tank.
  • Humic acid is a great addition to your system whether or not you have issues with algae. It’s great for your fish and your plants and can help chelate a number of important plant nutrients. The shading effect it exacts on algae in deep systems is really just a bonus


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