Do excess nutrients 'cause' algae?
Algae requires nutrients to grow, so the idea that if you have large amounts of nutrients in the water, algae will bloom more easily is an intuitive leap to take. However, nutrients alone are rarely the main factors triggering most algae blooms.
In a similar analogy, Does eating additional protein on a daily basis make one fat? It depends - if a person is leading a sedentary lifestyle with little energy output, a net increase in daily calories through increased protein intake will lead to fat gain. However, a person on a muscle building gym program will benefit from the increased protein - building muscle mass and increasing net calorie burn rate; eating addition protein in this case can lead to fat loss. Fitness/builders demonstrate this to the extreme - being extremely lean despite an increased intake of protein/calories. The situation is similarly non-linear when it comes to nutrient dosing and planted tanks.
Both algae and plants will grow faster if there are plentiful nutrients in the water. However, you will never get an algae free tank by limiting nutrients alone. Algae are microscopic and have much lower nutrient requirements to survive compared to aquatic plants. If plants don't do well because they are starving, it will lead to deteriorating old growth. The sugars and carbohydrates released by deteriorating leaves trigger algae spores that feed off these substances. This is why it is common to see algae attaching to older growth and plants that are not growing well. The opposite is also true; healthy plants are extremely algae resistant. Filling up a tank full of healthy plants is the easiest way to get a good head start in planted tank algae control.
Whether you choose to dose more nutrients or less, minimally you must dose enough to ensure that plants are healthy and growing well. Healthy plants are extremely algae resistant.
In planted aquariums where there is dominant healthy plant mass, nutrient levels in the water column can be maintained at high levels (non-limiting for both plant and algae) yet we can have algae free tanks. This has been demonstrated consistently by well-run tanks by Tom barr and others using the EI method of dosing - where nutrient levels remain consistently high throughout the week ( at no point do plants consume all the nutrients available in the water ), yet we get the twin blessings of good plant growth and algae free tank.
Tom barr's tank above demonstrates that having plenty of nutrients in the water does not result in an algae filled planted tank; if there is attention to plant health and overall tank cleanliness.
Does this mean that we should maintain high levels of nutrients in all tanks?
Of course not. If you have a tank that is fully planted, such as Tom's tank above, plant dominance allows the tank to be greatly algae-resistant. In tanks that are more sparsely planted, heavy fertilizer dosing can be destabilizing. In the event that algae spores are triggered, and there is a lack of plant mass available to deny the algae space to flourish, algae will spread more quickly given the elevated nutrient levels.
Iwagumis with only delicate carpets, and hardscape focused aquascapes that have large areas of open sand and rock rock have much lower nutrient requirements compared to heavily planted tanks filled with stem plants. They also have less dominant plant mass to deny algae a home. For those with Iwagumi style and hardscape style planted tank, a combination of lean dosing and good maintenance is an important step in planted tank algae control. They look deceptively simple, but actually require more experience to manage and balance compared to more fully planted tanks. Dosing fertilizers heavily in this style of tanks creates instability and is not something I would recommend. What to dose more of, and what to dose less of is covered in the nutrient dosing section of this site.
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