While a certain amount of algae is to be expected in an aquaponics system, particularly in the grow beds, too much can indicate that the system is out of balance and can cause problems with water chemistry, equipment, and more. To understand how algae can have such a large effect, it’s important to understand how it’s involved in the nutrient cycle.
Organic waste, whether it’s from fish excrement, plant cells, dead bacteria, or dead algae, should decompose relatively quickly through the action of “good’ bacteria. These bacteria convert ammonia to less toxic ammonium, as well as converting nitrites into nitrates. Both ammonium and nitrates are nutrients for the plants in the system and are used in the process of photosynthesis. Ideally, the production of nutrients from waste products will match the nutrient requirements of the plants, and the system will remain in perfect balance. Algae comes in when there is an excess of nutrients available, or when other conditions exist that give it an advantage over established plants, such as an abundance of direct sunlight. Aside from taking away nutrients that the crop plants need, algae can wreak havoc with oxygen levels and pH levels, particularly in the cycle from day to night and back again. If a large amount of algae dies off suddenly, levels of ammonia and nitrites will rise rapidly and create a toxic environment for both fish and plants. Aside from the chemical mayhem, algae can gum up the pumps and pipes and water feeds, which leads to lots of extra maintenance. If you are having trouble with algae growth, the first (and best) course of action is to tweak your nutrient levels. Adding more plants, reducing fish populations, or feeding the fish less will all either lower the amount of organic waste produced, or increase the uptake of nutrients. Providing some shade from direct sunlight, if that’s not detrimental to your plant production, can also help, since algae are able to reproduce rapidly in high light levels.
