How to control fuzz/hair/thread algae (filamentous algae)

Although there are different types of filamentous algae, they all have similar basic causes and triggers. 

3 main causes:

• Long term poor plant health due to poor Carbon/nutrient availability.
• Plant stress due to being moved or freshly planted.
• Ammonia spike coupled with high light.

Healthy plants produce defensive chemicals that prevent algae from attaching. Weak or stressed plants excrete waste metabolites from their leaf margins which actually encourage algae to attach. In any planted aquarium, maintaining good plant health is the basic defence against algae.

Healthy plants remain algae free even in environments with lots of available light and nutrients. 

Plants can become unhealthy if growth conditions are too low. This can happen in a number of ways. In aquasoil aquariums it can happen when the aquarium soil is depleted and the plants are deprived of nutrients. In low-tech tanks without CO2 injection, it can also happen when the soil is depleted - not from a nutrient point of view, but from the point of view of less CO2 being generated compared to fresh soil.

Filamentous algae can also be triggered by short-term shocks to the aquarium environment, such as a spike in ammonia or organic waste, or other parameter shocks.

Plants can show signs of growth even under stress - an unstable aquarium can still show normal plant growth. Signs of stress include; algae on leaves, premature shedding of older leaves and uneven growth.

When left unattended, deteriorating leaves combined with high light levels can result in algae ( thread / hair algae above, for instance) taking over a tank completely. 

General Causes

• Unhealthy, deficient, or stressed plants (sub-optimal CO2, nutrient issues, overcrowding, transplant shock, physical damage, over-pruning stress, unstable or extreme tank parameters).
• Abundance of old, deteriorating growth.
• Spike in Ammonia source in tank. (terrestrial osmocote, uncycled tanks, heavy feeding, nutrient formulas that contain Ammonia, dead livestock)

Solutions

• Improve plant growth parameters.
• Replant healthy tops and discard old growth.
• Mild cases would generally disappear by themselves as plant health and tank stability improves.
• Severe cases can be killed off by APT Fix & other commercial algicides but base causes need to be addressed or the algae may return.
  
• Large water changes and clearing of organic debris from substrate.
  

Click on this page on how to change water for planted tank.