Do excess nutrients trigger algae growth in a planted tank?

Do 'excess nutrients' trigger algae?

Algae need nutrients to grow, so it is an intuitive leap to think that if you have large amounts of nutrients in the water, algae will bloom more easily. This depends on the type of nutrient - not all elements have the same effect on the ecosystem. Not all 'nutrients' are created equal. For example, 100ppm (parts per million) of calcium or potassium will have no effect on the presence/absence of algae in tanks, but even small ammonia spikes can trigger algae - so a recirculating tank with a mature bio-filter will help. There is generally little disagreement with these observations among aquatic growers.

People wonder more about the role of nitrates, phosphates, iron - does an excess of these elements cause algae?

Both algae and plants grow faster when there are plenty of nutrients in the water. Algae are microscopic and have much lower nutrient requirements to survive than aquatic plants. If plants don't grow well because they are starving, the result will be decaying old growth. The organic waste proteins released by decaying leaves trigger algae spores that feed on these substances. This is why it is common to see algae on older growth and plants that are not growing well. The opposite is also true; healthy plants are extremely resistant to algae. Filling a tank with healthy plants is the easiest way to get a good head start on 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. This is true for all scenarios.

In planted aquariums where there is a dominant healthy plant mass, nutrient levels in the water column can be maintained at high levels (non-limiting for both plants and algae) and 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 ).

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 fully planted tank, such as Tom's above, the dominance of plants will make the tank very resistant to algae. In more sparsely planted tanks, heavy doses of fertiliser can be destabilising. If algae spores are released and there is a lack of plant mass to deny the algae space to thrive, the algae will spread even faster due to the increased nutrient levels.

Green Dust Algae (GDA) is very common in EI tanks if the tank is not mature enough or does not have enough plant mass, for example. Algae problems in these tanks can be much worse than in tanks where the water column is nutrient poor.

Iwagumis with only delicate carpets and hardscape aquascapes with large areas of open sand and rock have much lower nutrient requirements than heavily planted tanks filled with stem plants. They also have less dominant plant mass to deny algae a home. For those with Iwagumi and Hardscape style planted tanks, a combination of lean dosing and good maintenance is an important step in planted tank algae control. Hardscape heavy tanks also generally run lower light levels.

Such tanks look deceptively simple, but actually require more experience to manage and balance than more fully planted tanks. Heavy dosing of fertiliser in this style of tank creates instability and is not something we would recommend.

In hardscape centric competition aquascapes such as this scape by Luca galarraga, overwhelmingly, the chosen dosing approach is lean water column dosing (low NO3, PO4 values) and substrate feeding plants by using rich aquasoil in planted areas. This is to make sure the hardscape is keep as clean of green dust/spot algae as possible.

What to dose more of, and what to dose less of is covered in the nutrient dosing section of this site.