How Long Does it Take for Algae to Grow in Fish Tank?

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Nobody wants to see algae in their aquarium, but everybody will eventually. This isn’t necessarily bad because algae are beneficial in an aquatic system in moderate amounts.

They serve as food for many varieties of aquatic animals like plecos, catfish, shrimp, snails, and many other fish species.

But what happens if the algae overwhelm the environment, which type grows first, and how should you manage the problem? We’ll discuss these points and more in the following article.

How Long Does it Take for Algae to Grow in Fish Tank?

Algae are sensitive to ammonia and nitrites and consume nitrates as their favorite food source.

These facts alone should tell you the exact moment when algae begin to grow in a fish tank, which is when the tank cycle is complete.

Every aquarium needs to undergo a cycling process to stabilize the water’s chemistry. The nitrogen cycle aims to promote the growth of Nitrosomonas and Nitrobacter bacteria which convert ammonia and nitrites into nitrates.

Once the ammonia and nitrites fall to 0 and nitrates remain stable below the 20-ppm mark, you can consider the cycling process complete.

That’s when algae will begin to develop in the tank, approximately 15-30 days after the cycle’s start.

What Type of Algae Grow First?

There isn’t a specific type of algae that grows first in any fish tank. It depends on the environmental resources, temperature, nutrients, etc.

Generally, though, diatoms (brown algae) are considered to be the most prevalent type of algae in most aquariums.

Green algae, hair algae, blue-green algae, and other types are also decent contenders to consider in this sense.

In truth, your aquarium may struggle with different types of algae; fortunately, you can eliminate and prevent them all via the same approaches. We’ll discuss these shortly.

What is the Fastest-Growing Algae?

The algae’s growth rate is influenced by the environmental conditions available. These include lighting, water nutrients, temperature, and dissolved oxygen, among other things.

So, there isn’t a specific strain of aquatic algae that grows faster than others.

It all boils down to which algae gets to develop first and the overall environmental conditions.

This being said, it turns out that green algae may have a slight edge in this sense, although research is not definitive.

Things that Affect Algae Growth in Fish Tank

Some aquatic systems are more prone to algae overgrowth than others. Fortunately, there are always markers highlighting the vulnerabilities contributing to the issue.

Some of these consider:

  • Excess organic matter – Maybe you overfeed your fish and crease excess food residues and fish waste. Or maybe you fail to clean the tank properly, leaving plant matter to rot in the water. This excess organic matter will eventually lead to nitrate boosts, supporting the colonies of brown and green algae waiting to bloom. Keeping the environment clean will diminish the algae’s ability to grow and spread.
  • The dissolved CO2 – Plants require CO2 to perform photosynthesis during the day. Some plants require more CO2 as they grow larger and have a faster growth rate. Fortunately for you, algae cannot survive in high CO2 environments, so you can use CO2 injections to feed your plants and eradicate the algae colonies. Just be careful about it; fish cannot breathe CO2, so the surplus can cause them to suffocate. Especially since plants themselves produce CO2 during nighttime when the photosynthesis process is reversed.
  • Light intensity – Algae require high light conditions to bloom. Reducing the light intensity will inhibit the algae’s developmental process.
  • Water currents – Algae require stale water since water currents prevent them from retaining their physical composure. So, a more powerful filtration system will prevent the algae from latching onto different hard surfaces and sucking in the floating algae spores constantly. This will keep the water cleaner and prevent algae deposits over time.

These are all interesting facts, but what about prevention? It’s far easier to the algae bloom than struggling to restore an algae-infested environment. So, let’s get into that!

How to Reduce Algae Growth in Fish Tank?

Consider the following:

  • Reduce the light – As we’ve already discussed, algae are photosensitive, so they require light to grow properly. This can lead to a conflict of interests because your live plants also require light to perform photosynthesis. Fortunately, they need a lot less light than algae. Find the sweet spot based on your plant species, and algae will no longer be a problem.
  • Reduce the use of liquid fertilizers – Floating plants require liquid fertilization for proper nutrient intake. There’s no way around it, unfortunately, especially in high-tech aquariums with many live plants. The problem is that liquid fertilizers promote algae growth. Learn how much fertilizer your plants need and stick to the recommended amounts. This way, your plants will consume all of the available fertilizer and leave nothing for the algae.
  • Add more plants – Nothing turns off algae more effectively than a bit of competition. Add more plants and they will consume all the available nutrients, starving the algae and preventing them from ever taking off.
  • Add more algae eatersAlgae eaters are a must in any aquatic setup. You need a reliable cleaning crew to keep the tank clean and safe, so consider species like catfishes, snails, shrimp, platies, tangs, and many other fish specialized in algae eating. Plecos and Amano shrimps are probably your best options since these are professional algae grazers with a great pedigree under their belt.
  • Scrape algae deposits manually – It’s always good to perform regular cleaning to keep the algae development in check. You can clean any visible algae deposits on the tank’s walls with a sponge and let the filter suck in the floating algae spores.
  • Clean and disinfect plants and tank decorations – You may sometimes need to clean rocks, driftwood, decorations, and plants if they become covered in algae with time. You can remove each piece gently from the tank, clean them thoroughly with a brush, rinse with tank water, allow them to dry, and place them back into the tank. When it comes to your floating plants, douse them in a bleach solution for a couple of minutes. Use 1 part bleach for 20 parts of water for best results. You can also use potassium permanganate and hydrogen peroxide for the same purpose.
  • CO2 injectionsCO2 injections are great for plant growth and for inhibiting algae development. Just use CO2 injections with caution in fish tanks, given the dangers associated with high CO2 levels.
  • Have a stable maintenance routine – Remove fish waste, food residues, and decaying organic matter and avoid overfeeding your fish. Vacuuming the substrate every several days and changing the tank’s water once a week will work wonders in terms of preventing algae bloom.

Ultimately, your best tool against aquarium algae is constant monitoring. Keep track of the algae’s development and take measures whenever they overstep their boundaries.


Algae are generally safe for fish and plants since they don’t alter water chemistry. However, they can become dangerous when mature, as they can cover plants and restrict their access to light in the process.

Hair algae can also entangle fish and kill them via suffocation because fish need to swim to breathe properly.

Fortunately, you won’t have to struggle with any of these scenarios. Follow my guide, and algae won’t be a problem worthy of mentioning anymore.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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