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Algae Control 101: How to prevent algae in an aquarium?

December 05, 2022 10 min read

Algae Control 101: How to prevent algae in an aquarium?

Algae removal techniques should not be the default method to keep a tank algae free. The cleanest tanks are where algae does not spawn in the first place. This means avoiding the key triggers for algae - nitrogenous waste, ammonia, unhealthy plants. Read more on algae triggers here.

Maintaining good plant health, and stable parameters are important as it allows plants to grow consistently healthy. Healthy plants produce anti-microbial chemicals that prevent pathogens and algae from attacking the plant. However, each time growth parameters are changed drastically, plants have to channel energy instead to re-program their enzymes to optimize for new conditions.

For example, if an aquatic plant was transferred from a tank with high CO2 (carbon dioxide) levels to a tank with low CO2 levels, the plant would channel more energy to proteins and enzymes responsible for capturing CO2 to compensate for the dip in CO2 levels. While the plant goes through this adaptation phrase, it prioritises critical functions, leaving less energy to produce defensive anti-microbial chemicals.

Under stress, plants will generally stop defending the older, less valuable leaves first. Algae will then opportunistically spawn on the affected (usually older) leaves. If the plant recovers in time, often affected leaves can recover. However, often the plant may choose instead to channel energy into producing new leaves, sacrificing the oldest leaves. Old leaves do not heal, and need to be trimmed away to make space for new growth. Preventing the plant from under going such periods of stress is important in keeping the tank algae free.

Most planted tanks produce a lot of organic debris that can trigger algae. Having shrimps, snails and microfauna that quickly break down and digest these smaller pieces of organic material is tremendously useful. Regular vacuuming of the top surface of the substrate also important; using a turkey blaster to stir up only the top most layer of the substrate while hovering a siphon above is an easy way to accomplish this.

4 main factors

There are 4 main factors that determine algae absence or presence in a tank.

Light Control

Healthy Plant Mass

Tank Cleanliness

 Biological Maturity

Light Control

Using very strong lighting is like driving a fast car. It could get you to your destination more quickly, or end in an accident. Strong lighting coupled with organic waste or damaged plants trigger algae spores to bloom and the end result is visible algae in the tank.

However, our plants also require sufficient light to grow well, hence controlling aquarium lighting is a balancing act necessary to achieve continuous success in planted tank algae control.


This is a guide to the appropriate light intensity as measured on the surface of the substrate (more details of how to measure this in the light section)

  • 30umols of PAR (photosynthetic active radiation): Low light plants such as ferns, mosses, Cryptocoryne, Anubias, Bucephalandra species grow well. If you are growing purely shade plants, it is smart to stay in this range.
  • 50umols of PAR will enable you to grow any commercially available aquatic plant (when coupled with optimal CO2 levels). However, this gives little allowance for shading issues in crowded tanks. Most nature style and Iwagumi style tanks that do not require high density do well at this range. 
  • 50 to 150umols of PAR; Colored stems will display better coloration and carpets spread very fast as light levels increase, at the risk of more algae issues. Tank cleanliness and plant health must be maintained at optimal conditions to prevent run-away algae. Allows for increased planting density for light demanding plants. Most experienced aquarists can do well in this range with regular upkeep.
  • 200umols of PAR & above; Marginal gains to plant growth form and coloration starts to be outweighed by large potential instability of algae outbreaks. Might be useful inducing stronger coloration in shorter stems close to substrate; and for farming purposes. Should only be used by aquarists used to maintaining already algae-free tanks.

Proserpinaca palustris

Proserpinaca palustris is one of the few plants that see improvement in coloration/form with very high light levels. Most colored/red plants can be grown well without such excessive light.


  • Minimum of 5-6 hours for new tanks that want to minimize triggering algae.
  • 7-10 hours is common for average, stable tanks.
  • 10+ hours; marginal gains to plant growth rates, increased chances of algae incidence. Suggest using moonlighting/lower powered display lighting if extended lighting hours is desired for viewing purposes.

Having an adjustable light system gives flexibility. Changing the number of hours as well as intensity, by using dimmers or hanging kits, can change outcomes considerably. If you do not have plants that require high lighting, using lower amounts of light to achieve aquascaping goals is much more stable and require lower maintenance.

power timer

Power timers plug into standard power outlets and allow easy programming of when lights turn on/off.

For fish-only tanks with no plants - (5-7days) blackouts are an easy solution to get rid of algae. As algae do not have the larger starch storing structures of more advanced plants, they die off quickly without light.

Healthy Plant Mass

It is critically important to plant densely at the start well and ensure plant health by having adequate carbon, nutrients, light and flow. Lack of carbon (in the form of Carbon dioxide) is the most common variable that people fail to optimize. This is why "low CO2" is cited as the cause for many types of algae; higher CO2 levels by itself has no impact on algae, algae is not killed off by high CO2 levels. The impact is transmitted through the change in overall tank environment due to improved plant health as plants get the CO2 they require to grow robustly.

Dennis Wong farm tank PAR reading

Even slow growers such as Bucephalandra are algae resistant if they are healthy - these receive high light levels in our farm tank (200ish umols of PAR) , but remain algae free.

Recommended plant mass as percentage of tank space

  • Planted aquariums with 70%+ of surface substrate planted are much more resilient against algae
  • Planted aquariums with 30% and less of surface substrate planted are very vulnerable to algae; cleanliness becomes paramount to avoid algae triggers.
  • Larger, more robust plants (swords, lotuses, crinum) are more resilient against algae than smaller plants (carpets & mosses).
  • Fast, aggressive growing plants (water wisteria, large stem plants) are more resilient than slow growers (java fern, Anubias, Alternanthera reineckii).
  • Due to tank design and flow patterns, some tanks may have algae localized only in a certain area of the tank. Planting larger, more robust plants in those areas can solve persistent algae issues.

Plant health

  • Decaying leaves attract algae like flies to a carcass. Take the time to remove them.
  • Adequate nutrients and CO2 are necessary for good plant health long term.
  • Over-crowding leads to poor plant health and quicker decaying old growth. Prune consistently; a tank fully filled with new growth is extremely algae resistant.

 Dou Mok

An example of a lightly planted tank by Dou Mok. The plant selection is also one that is most vulnerable to algae issues. (ferns, mosses and anubias). The fact that they remain algae free is a testament to the high maintenance standard of the aquarist. Such designs seem deceptively simple, but in fact take a lot of expertise to manage to maturity. Vacuuming substrate debris, removing dead and decaying leaves and pruning over-crowded growth are all important actions in tank maintenance. Many hobbyists tanks start out lightly planted, and require more water changes and maintenance work to remain algae free.

Mark Crow Dutch Style

Mark crow's planted aquarium on the top is an example of a heavily planted tank. In tanks where nearly 100% of the available space is planted with healthy plants, managing algae should be a breeze.

"My plants are growing, so surely they are healthy?

Unfortunately, no... you can have plants that are visibly growing, and getting larger, but they can still be unhealthy or in a state of stress. They can grow but be nutrient deficient in cases where nutrient dosing is lacking, but more commonly unhealthy/stressed plants occur due to steep fluctuations in water parameters or nutrient dosing.

Plants will reprogram their enzymes to make the best use of current parameters. For example, if you suddenly allow CO2 levels to dip, plants will need to reprogram their internal structures to make do with the less available CO2 - devoting more proteins and energy to CO2 capture than say light capturing functions. The waste proteins are then ejected directly on the leaf/plant surfaces; this organic waste becomes the signalling mechanism for algae to spawn. The same thing happens when water parameters or nutrient availability fluctuates in a big way.

Robust plants can deal with such changes more easily (they are more adaptable) while some delicate plants that can survive in a narrow range of values will have faster deterioration of older leaves or melting. Thus, it is important to not only supply what is sufficient for plant growth needs, but to also to do it in a consistent manner over time. This is one of the reasons why it is recommended to do nutrient dosing a few times throughout the week, rather than in one large dose per week.

Take for example, both sets of Rotala macrandra below; they are both "growing", but the difference in state of health are apparent. Even ignoring color differences (which may be due to light or photography methods), observe the differences in - thickness of stem & leaves, internodal distance, state of growth tips, uneven leaf coloration vs even, full colored leaves. Weak plants are algae magnets.

Aquarists that try growing very difficult plants that have a narrow set of requirements will also face more algae issues down the road. If you are a beginner or new to planted tanks, choosing more robust species definitely makes life easier, and makes the tank more forgiving to fluctuations in parameters.

plant comparison

Difficult species = harder job to maintain good plant health = harder time with algae

The tank below is the exact scenario that beginners should avoid; growing species that require soft water (Trithuria lanterna) directly beside species that prefer hard water (Pogostemon helferi) and having high percentage of delicate plants that are vulnerable to algae. Also, growing shade plants (Bucephalandra) beside plants that prefer high lighting (Red Eriocaulon, Rotala florida, Trithuria lanterna) makes the Bucephalandra more vulnerable to algae.

Dennis Wong Bucephalandra blood vomit

Plants with more stringent growth requirements are also more vulnerable to algae by definition as many folks may not be able to satisfy their needs adequately (which leads them to grow in a stressed state). Having a larger percentage of robust plants mixed with a couple of difficult species make it easier to maintain the tank overall. If you are just starting out; avoid purchasing too many difficult species at one time; expand your collection slowly and give yourself time to understand the needs of each plant. If you have persistent algae issues with only a certain species or type of plant, changing to something else more robust is an easy way to side-step the issue. Sometimes changing the location where a difficult plant grows in the tank will work also - it may need a tad more flow or light that is available in a better spot.

Grow plants that favor similar water parameters makes the job easier. Attempting to mix species which have very different growth requirements; for example, mixing soft water species with species that prefer harder water can make it difficult to keep all plants happy at the same time. Mixing Sygonanthus & Tonina species (which both prefer very soft water) with Pogostemon helferi (which prefers harder water) makes balancing parameters tricky. When in doubt, check before buying plants.

Biological Maturity & Tank Cleanliness

Following the same train of thought that decaying plant matter triggers algae blooms, organic waste (whether by livestock or plants) is one of the key triggers for algae blooms. Having efficient bio-filtration and a matured tank environment leads to quicker break-down of organic waste and ammonia, minimizing trigger time for algae. This means that having an environment that promotes microbial activity, that allows bacteria to break down waste products more quickly & efficiently has a large impact on the tank environment.

​These microbes are delicate and heavy usage of harsh chemicals (like algicides) will affect them. This is why many aquarists get caught up in the never ending loop of killing algae - having new algae - looking for new cures, whist never having the tank in a sustained period of being algae free. Prevention is better than cure - if you dose algicides, spot dose them in problem areas early, rather than nuke the whole tank.

Step 1: keep organic waste low

Ways to manage organic levels:

  • Never over-stock a tank in its early months. Livestock waste contributes significantly to algae issues in new tanks. (new meaning less than 3 months old).
  • Regular water changes (30-50% weekly).
  • Removal of old/decaying growth. This requires topping and replanting - cutting off and replanting the top portion of stem plants, while discarding the deteriorating bottoms.
  • Cutting off damaged leaves, and removal of floating debris.
  • Weekly/fortnightly light substrate vacuuming with turkey baster to remove surface debris.
  • Servicing clogged filters. Depending on your bio-load this could be done as frequently as every fortnight or up to every 3 months. Using a filter with an easy to remove pre-filter chamber that does not require dismantling of the whole filter is an easy way to make maintenance easy.

Step 2: practice regular cleaning

Water changes are not enough; good vacuuming techniques to remove detritus is important. Watch the following video for the technique:

More detailed steps on how to maintain aquasoil substrates long term here.

Step 3: create effective biofiltration

Steps to setting up a system that has effective bio-filtration:

  • Maintain high oxygen levels in the tank through sufficient gaseous exchange mechanisms. This is done by usage of surface skimmers and flow patterns that exchange surface layer of water with deeper layers in the tank. Higher oxygen levels is important for bacteria activity.
  • Using organic/soil-based substrates or appropriately sized sand (2-3mm) in the tank rather than inert large sized gravel. Increased porosity allows better bacteria colonization.
  • Having a decent filter and good flow to bring debris to the filter.
  • Filter flow rate of 5X to 10X of tank size. 1000L/hr filter on a 200L tank for example.
  • Shrimps, snails and other critters that breakdown larger sized organic particles.
  • Maintaining stable water parameters long term. This also means avoiding spikes of toxic elements (heavy metal content in water for example)
  • Pre-cycling the tank using starter bacteria cultures/products. Old school versions did not function well; the newer ones work.

bloody mary shrimps

Shrimps, snails and other micro-fauna keep the tank clean by breaking down organic debris. This sand path with mixed carpets is more than a year old; fortnightly light vacuuming of the surface keeps it clean.

Many aquarists think that just because common water parameters (ammonia, nitrites) tests come up perfect that their water must be "perfect". This is not so as organic waste products come in many forms that don't turn up in the common hobbyist tests for ammonia or nitrites. Regular water changes remove the need for guesswork as to what is your actual water quality.

As tanks become biologically matured over time, organic waste breaks down more quickly. However, most tanks will take many weeks to reach a stable age - until then, large, regular water changes make sense.

You can watch microbes eat algae in the video clip below.

Here are links for further reading on the following topics:

1. Detailed steps to tank cycling

2. What nutrients do aquarium plants needs for growth?

3. Section on CO2 for planted tank

4. Section on aquarium plants care guides 

5. For detailed steps to control specific algae, click here.

6. More detailed steps on how to maintain aquasoil substrates here.