Dark Start Method for Aquarium – The Complete Guide

Disclosure: I may earn a commission when you purchase through my affiliate links. As an Amazon Associate I earn from qualifying purchases. – read more

As you know by now, every aquarium should undergo a cycling process before adding the fish. The process itself aims to balance the environment by allowing nitrifying and denitrifying bacteria to form. These organisms are vital for the tank’s long-term ‘wellbeing’ as they break down ammonia and nitrites and turn them into nitrates.

Nitrates represent one of the main sources of nutrition for plants.

This biological filtration process takes place in all aquatic setups, but it’s far more important in close systems like aquariums. That’s because closed systems don’t have the luxury of free chemical circulation, so ammonia will accumulate fast due to fish waste, food residues, dead plant matter, etc.

This is where the Dark Start cycling method comes in. You may not have heard about this one because it’s relatively new in the aquarium business. It’s actually so new that most people are still confused about how it works or whether it is effective. So, let’s dive into that!

What is the Dark Start Method?

The Dark Start method is a cycling procedure that aims to allow beneficial bacteria to form before adding the fish and plants. If this sounds familiar, that’s because it is. This method is similar to classical cycling procedures, where you add the substrate, fill the tank with water, and add ammonia regularly to promote bacterial growth.

The nitrifying bacteria will soon develop stable colonies, feeding on the ammonia and turning it into nitrites. Then the denitrifying bacteria form, further converting nitrites into nitrates, which are far less toxic for fish.

The difference between standard cycling methods and the Dark Start method is that the latter demands the absence of light and doesn’t need any added ammonia. Other than that, the procedure is just as easy, and it relies on time as the main asset.

But let’s assess the Dark Start cycle more in-depth.

The Process of the Dark Start Method

The Dark Start method’s cycling process lasts several weeks to a month. This timeframe is generally enough to produce a self-sustainable setup filled with colonies of beneficial bacteria. So, I advise only getting your fish and plants once the cycling process has been completed. There’s no point in getting them sooner, just to keep them in a temporary setup until the main tank is ready.

With this out of the way, here are the primary steps involved in the Dark Start method:

Consider the Substrate

You get the tank, and you get the substrate. The substrate should be fertilized plant soil-only since this method doesn’t work with sand, gravel, or any type of inert substrate. The fertilized soil contains sufficient nutrients to produce decay-related ammonia, triggering the emergence of nitrifying bacteria. You can also add any other aquascape components you might have, like rocks or various decorations.

The coming colonies of bacteria will cover any available surface they can find. I recommend porous lava rocks as the ideal design pieces. Lava rocks don’t alter the water’s chemistry and come with a highly porous surface – the ideal breeding ground for denitrifying bacteria and other microorganisms.

Pour the Water

Do it gently, as you shouldn’t stir up the substrate. This will cloud the water and disturb the landscape, flooding the water with debris and floating particles. This isn’t a problem necessarily, because the particles will eventually settle back on the substrate.

But you will be turning on the filtration system, and the filter will suck in all those floating particles before they get to settle. This can clog the filter, causing problems you weren’t ready for. You can pour the water using a smaller container or a hose, careful to aim the water flow down the tank’s wall to minimize splashing.

Cut the Light Off

As the method name suggests, no light is involved in the process. The concept is simple – and light promotes algae growth, especially since the environment is packed with nutrients. Algae require light to grow, and the more light there is, the better for them.

Since there are no plants, algae will grow uninhibited, consuming nutrients and destabilizing the habitat and bacterial colonies in the process. Cutting off the light source won’t allow algae to grow.

Just make sure you consider alternate light sources as well. If your tank is in a brightly lit room, it may not be enough to cut out the main light source. In this sense, I recommend placing black shades over the tank and covering the walls with a similar material. You should block as much light as possible.

Turn the Filter On

Naturally, you need a reliable filtration system in place for this method to deliver the best results. The filter’s purpose is to keep the water moving, improve oxygen levels, and allow the free circulation of nutrients. Water currents will get the nutrients out of the soil and feed the nitrifying bacteria in the water.

These microorganisms will soon grow, multiply, and develop into thriving colonies, soon to expand over the entire environment.

Water Changes are Necessary

Water changes are a must during the process since ammonia and nitrates build up faster than the nitrifying bacteria are capable of disposing of them. This is because there aren’t enough colonies of bacteria to stabilize the system yet.

So, you need to remove the excess ammonia via regular water changes. Some people suggest one massive water change of around 90% of the total water volume at the end of the cycling. Others, like myself, recommend gradual, 10-15% water changes every 2-3 days for the entire duration of the cycle.

I recommend monitoring water parameters and performing a partial water change whenever ammonia exceeds concentrations of 4 ppm. The same goes for nitrites, while nitrates require a water change when going over 20 ppm.

The Waiting Game Begins

Once everything is in place, you now have to wait for the process to end. For a clearer perspective on things, here’s how you know that the cycling process goes in the right direction:

  • Ammonia – Ammonia fluctuates over time and increases dramatically during the first several days. It’s common for ammonia levels to jump the 4 ppm mark, at which point you need to perform a partial water change. It’s important to keep ammonia levels below 4 ppm to prevent the chemical from killing off the colonies of good bacteria. Ammonia levels drop with time as the nitrifying bacteria convert it into nitrites.
  • Nitrites – These will also spike at first, following a similar path to ammonia. Denitrifying bacteria will convert them into nitrates which are far less toxic to fish. The more denitrifying bacteria there are in the environment, the faster the nitrite levels will drop.
  • NitratesNitrates are the end product and the ones that signal the completion of the cycling process.

Your goal is to get to 0 ammonia and nitrites and keep nitrates at around 10-20 ppm. That’s when you know that the cycling process is complete.

Pros and Cons of Dark Start Method

This is very much an uncharted territory, so there’s little I can offer you in terms of pros and cons. You can search the forums for people who’ve already tested the method and get some insight on what to expect.

Overall, the most I could gather falls along the following lines:

  • Pros – This is a self-sustainable method. You only need to get it going and mind your own business as the environment cycles itself. Sure, you will need to monitor water parameters and perform some water changes as ammonia and nitrites exceed the ideal parameters, but that’s about it.
  • Cons – The entire process lasts approximately 4 weeks. Then you have another 2-3 weeks of waiting time until plants to fully established in their environment. This accommodation period is natural for all aquatic plants as they adapt to their new environment.

In short, this is still a new method that requires more testing and insight to determine the right approach.

How to Tell if Fish Tank is Cycled?

You have 3 parameters to follow in this sense: ammonia, nitrites, and nitrates. The beginning of the Dark Start method will see ammonia and nitrites spiking as the nitrifying bacteria do their job. You may need to perform water changes occasionally to dilute the chemicals until the denitrifying bacteria take over the task.

These will then transform nitrites into nitrates, effectively closing the circle. Your tank is considered fully cycled when displaying the following parameters:

  • Ammonia – 0 ppm
  • Nitrites – 0 ppm
  • Nitrates – 10-20 ppm


The Dark Start method is easy to apply, but it takes more investigation to determine its actual success rate and the pros and cons to expect.

Fortunately, applying the method won’t cost you anything except time. After all, you won’t have any fish or plants in the tank during the cycle.

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.
Leave a Comment

Your email address will not be published. Required fields are marked *