Algae normally appears when there is an imbalance in nutrients, CO2, oxygen and light. For example, too much light but too few nutrients and CO2 will cause algae. Poor distribution of CO2 and nutrients is also a common cause of algae. It is talked about widely that that lowering nitrates and phosphates (two vital nutrients) will reduce algae outbreaks, when actually, algae thrives in a low-nutrient environment. This is a myth and should be avoided in planted aquariums.
Here are the main reasons why we get algae in our planted aquariums:
1. Low quantities of beneficial bacteria in a new setup
Algae often appears in the first 2-3 months in a new setup. This is because a newly established planted aquarium does not have enough beneficial bacteria to convert ammonia through the nitrification cycle. The excess amounts of ammonia will cause algae blooms. Algae smothers plants, blocking light and depriving the plants of nutrients and CO2 passing over the leaves. In aquariums with large amounts of algae, the plants will eventually die. To help the fight against algae during start-up you should be carrying out weekly water changes of 30-50%. This will reduce levels of organic waste (mainly ammonia) whilst your tank matures over the coming weeks. Remember, in a heavily planted aquarium that's well oxygenated by your plants (bacteria need plenty of O2 to build colonies), your tank will mature relatively quickly.
2. Poor water circulation
To ensure the nutrients and CO2 are circulating throughout the aquarium and reach all the plants, it is important to have strong water flow in any planted aquarium. It is widely agreed that the flow rate from your filters and powerheads should be around 10 times the aquarium volume to achieve sufficient circulation. I.e. for a 100L aquarium you should have a flow rate of 1000 liters per hour. Choose a filter with the right flow rate or add extra circulation pumps. When plants have sufficient access to nutrients and CO2, there is little left for algae to use.
3. Insufficient surface agitation
Surface agitation brings oxygen to the aquarium and helps prevent surface scum (oily film) from forming. However, too much surface agitation will also encourage gassing off any injected CO2. We recommend the use of an air pump, but only when the lights are turned off. Around 6-hours over night is a good amount of O2 diffusion.
Plants breathe in CO2 when the lights are on and begin using oxygen as soon as the lights are turned off. When the lights are turned off there becomes a lack of oxygen in the aquarium for the plants, fish and beneficial bacteria who then start to fight for the remaining oxygen. This causes beneficial bacteria to die off, resulting in increased waste products (ammonia) followed by algae attacks. Having good levels of both CO2 and O2 levels are important in a planted aquarium.
Note: under higher temperatures, oxygen becomes more and more depleted in an aquarium. You might need to supply more O2 and CO2 during the summer months.
4. An imbalance of light, CO2 and nutrients
The speed of which CO2 and nutrients are absorbed by plants depends on the amount of light supplied. The more light there is, the more CO2 and nutrients plants need. Think of light as the gas pedal in a car, and CO2 and nutrients as the fuel. The more you push down on the gas pedal, the more fuel is used.
It very often happens that aquarists supply too much light but do not provide enough CO2 concentration and nutrients. When this happens, plants suffer from growth deficiencies, 'melting' and algae blooms appear. Make sure that you measure CO2 levels using a drop checker when the lights are turned on and when they are turned off. This will give you an idea of whether you need to increase or decrease your CO2 dosing.
5. Poor aquarium maintenance
When regular maintenance is not carried out, organic waste starts to build up in aquarium which leads to a build up in ammonia for algae to thrive on. Regular substrate vacuuming and cleaning of the filter media will decrease the build up of organic waste.
Decaying leaves generate further waste products. Trimming plants of dead leaves will eliminate the ammonia source and promote new growth. Using a good set of aquaescaping tools will help you keep your plants in top condition.
A regular water change of 30-50% every week is encouraged to dilute the amount of organic waste in your water. This will reduce the concentration of waste products in your water which algae can thrive on.
6. Low population of algae eating animals
The Amano shrimp has become known as the best algae eating shrimp for planted aquariums. These shrimp are very good at eating hair algae as well as consuming uneaten fish food and breaking down fish waste which helps speed up the cycle. We would recommend 1 shrimp per 5 liters of water.
Snails can also have a roll in the clean up process, however they can be more invasive thean shrimp as they can quickly reproduce and become pests (depending on the species). Assasin snails eat other snails, and can be used to keep the populations down whilst still benefiting from their uses when fighting algae.