How to Grow Good Bacteria in a Fish Tank: 8 Steps

How to Grow Good Bacteria in a Fish Tank_ 8 Steps

Growing healthy bacteria in a fish tank is mission-critical for maintaining a healthy aquarium. Here you will find a step-by-step guide to making sure that you are growing healthy bacteria in your fish tank.

How do you grow healthy bacteria in a fish tank? There are 8 steps to growing healthy bacteria in a fish tank:

  • Make sure you have a proper filter in the tank
  • Introduce starter fish into the tank
  • Maintain temperature for bacteria growth
  • Turn Off UV-light above the tank
  • Test the water chemistry
  • Maintain the pH level of the water
  • Speed up the process by adding good bacteria manually
  • Speed up the process by adding habitat for bacteria

The good bacteria in a fish tank are nitrifying bacteria that break down toxic ammonia and nitrite. An alternative method for growing good bacteria will be discussed. It is possible to grow healthy bacteria in a fish tank without adding starter fish, but this technique presents its own challenges, which will be discussed in this guide.

What Are The Good Bacteria In A Fish Tank?

The good bacteria in the fish tank aren’t that different from those in our digestive tract. Good bacteria help to break down waste and clear out toxins. In short, these helpful bacteria are going to help keep your water clean and, therefore, your fish healthy.

Nitrifying Bacteria

There are two types of nitrifying bacteria that you want thriving in your freshwater fish tank. These bacteria are critical for the nitrogen cycle to roll smoothly within the tank.

As we know, too much ammonia is toxic to the fish, as are nitrites in large quantities. Fish eliminate ammonia from their blood through their gills. When they excrete ammonia, they are also releasing nitrogenous waste.

Fortunately, some bacteria like to eat that waste. And they are the same bacteria that are beneficial to your fish: nitrifying bacteria.

The two types of nitrifying bacteria you want in your fish tank are:

  • Nitrosomonas: These bacteria break ammonia down into nitrites
  • Nitrobacter: These bacteria break down potentially harmful nitrites into nitrates

Fish have a layer of mucus over their scales that protect them from small concentrations of ammonia, but they are susceptible to higher concentrations of ammonia. It can build up in their bodies and “burn” their gills. Their gills may appear to be bleeding, as you’ll begin to see reddish streaks near the gills.

Nitrogen compounds can rise to dangerous levels in a freshwater fish tank quite quickly. You will want to establish colonies of good bacteria in the filter bed of your aquarium that converts ammonia into nitrites and nitrites into nitrates.

But where do you get these bacteria?

Where to Find Nitrifying Bacteria For Your Aquarium

According to this article from Duke University, the desired species of nitrifying bacteria for cycling your aquarium can be found everywhere, including the air.

These opportunistic bacteria are awaiting an opportunity to be attached to an environment they can thrive in, such as the filter bed of your aquarium.

Nitrifying bacteria are not a product that aquarium owners necessarily need to purchase. Rather, you will attract good bacteria to your fish tank by going through the process of setting it up.

1. Check Which Type of Filter You Have in Your Water Tank

Every species of nitrifying bacteria needs an adequate supply of micronutrients in the fish tank in order to survive and thrive. Most critical of all is the need for phosphorus to provide energy for cellular functions. Phosphorus generally exists in fish tanks in the form of phosphate (chemical formula PO4).

Nitrobacter bacteria, which are responsible for breaking down harmful nitrites into nitrates, are hit particularly hard when there is not a healthy supply of phosphate in your fish tank.

Typically, a sufficient level of phosphate can be found in your drinking water. However, the filter in your fish tank may determine how much phosphate is made available to the bacteria in your fish tank.

High-tech water filters have become increasingly popular over time in the home aquarium industry. The high tech water filters are able to perform advanced purification procedures on the water in the fish tank, including de-ionizing, distillation, and reverse osmosis.

Unfortunately, these high-tech water filters may strip the water of essential nutrients such as phosphates if they are used improperly.

High-tech water filters do an excellent job of purifying the water in a fish tank but using them may require you to consider other options in the extreme case that nitrifying bacteria are unable to thrive in your fish tank.

How Do I Know How Much Phosphate Is In My Fish Tank?

You can find out how much phosphate is in your fish tank by using a phosphate test kit, such as the one found in the link. Generally, phosphate levels are not as much of a concern in fish tanks as other chemical parameters such as ammonia, nitrate, and acidity.

Phosphates are more of a concern in saltwater tanks with coral reefs in them, according to this article. This is because coral reefs are used to living in low nutrient conditions.

Fish will usually adapt to changing nutrient conditions. The main concern with phosphate in freshwater fish tanks is that there is enough phosphate present for nitrifying bacteria to grow.

2. Introduce Starter Fish Into The Tank

Your first step in cycling your fish tank will involve introducing good “starter fish” into the brand new aquarium environment. The reason you want these fish is that you want to give the good bacteria something to eat: ammonia from fish excretions.

“Starter fish” are defined as species that are hardy, easy to manage, and inexpensive. These species of fish will be the first to introduce ammonia to the tank, which the bacteria will then feed on.

You should introduce only one or two individuals of these species at the start. By adding more than one or two fish at the start of the aquarium’s life, you will run the risk of causing the nitrogen cycle to spin out of control.

Good starter fish for freshwater aquariums include:

  • Common Goldfish (for cold water tanks, can be kept in an unheated aquarium)
  • Zebra Danios (for warmer tanks)
  • Barbs (for warmer tanks)
  • African Cichlids (for warmer tanks)
  • South American Cichlids (for warmer tanks)

You should avoid using feeder fish for your aquarium because they can often introduce diseases to your fish tank, according to this article. Stick to the types of fish above and don’t bring in too many at once.

Alternative Method: Cycling A Fish Tank Before Adding Fish

With a little patience, you can cycle your fish tank without adding fish first to be a source of ammonia. You can add ammonia manually to attract nitrifying bacteria.

The downside to this method is that it is more difficult than adding fish to provide a steady supply of ammonia. With this method, you will need to constantly monitor the water chemistry using the test kits described earlier in this article.

How to Get Healthy Bacteria in an Aquarium Without Adding Fish?
You will need to manually add ammonia by using a form of ammonia such as ammonium chloride. You can find ammonia chloride sold in a form specifically designed for use in aquariums. Dr. Tim’s Aquatics makes a solution of ammonium chloride for fishless cycling that can be found here.

If you use a different source of ammonia, you will want to use a source of ammonia that doesn’t contain any added colors, perfumes, or detergents that can harm fish or the bio-filter component.

  • You should add enough drops of ammonia chloride to achieve a concentration of ammonia in the tank of 4-5 ppm.
  • You can find the approximate concentration of ammonia in the tank by using ammonia test strips.
  • You can add the ammonia all at once, or you may consider adding a few drops each day in order to have more control over the process – check here.

Monitor Nitrite And Nitrate Levels

Monitor nitrite levels by using nitrite test strips to test for the presence of bacteria that break down ammonia into nitrite. Then you will need to begin monitoring for bacteria responsible for breaking down nitrites into nitrates. You will want to continue monitoring ammonia levels during this entire process.

Ammonia levels should be monitored daily. You will want to make sure that you add small amounts of ammonia into the tank when the ammonia levels drop to 0 ppm. It is important not to cut off the cycle. Once it is clear that the fish tank is cycling, you can start to add a few fish after performing a water change.

Changing the Water Before Adding Fish

Before you add your first fish to the tank, you will need to change out some of the water to remove excess nitrate and ammonia in the tank.

Add fish when you have determined that the ammonia levels are continuously dropping during the day, and the nitrite levels are at 0 ppm, as is recommended here.

You will typically want to remove at least 50% of the water in the tank.

  • Slowly remove water
  • While removing the water, continue to monitor the ammonia and nitrite concentrations
  • Add a few fish to the tank within a few hours of removing water from the tank.

3. Maintain an Optimum Temperature

Nitrifying bacteria have temperature preferences, just like the fish themselves have temperature preferences. The optimal temperature range for the growth of nitrifying bacteria is approximately 75-85 degrees Fahrenheit, according to Pond Trade Magazine.

This doesn’t mean the nitrifying bacteria won’t grow in lower temperatures, but it will take longer for the nitrogen cycle to occur in fish tanks with cooler water than it will in tanks with warmer water.

The growth rate of nitrifying bacteria is cut by 50% when the water temperature is set at 65 degrees Fahrenheit. Growth is cut by 75% at approximately 50 degrees Fahrenheit.

A similar decrease in the growth rates of nitrifying bacteria in temperatures greater than 85 degrees Fahrenheit. By the time the temperature reaches 120 degrees Fahrenheit, the nitrifying bacteria will be dead.

These numbers say that if you want the nitrogen cycle to occur smoothly, then you will want to keep the temperature of your fish tank somewhere in the range of 65 to 85 degrees Fahrenheit.
Ultimately though, you should keep the tank set at the temperatures that the fish you keep in your tank prefer.

How Do I Check And Maintain The Temperature Of My Fish Tank?

You can find thermometers for your fish tank that will stick to the side of your aquarium. These specialty thermometers, such as the LCD digital aquarium thermometer, are affordable ways to ensure that the desired temperature range is being met.

4. Turn Off Bulbs Emitting Blue And Ultraviolet Light

Species of nitrifying bacteria are sensitive to different types of light. They can be especially sensitive to blue light and ultraviolet light.

The time period that nitrifying bacteria are sensitive to this light is limited to the time before the bacteria colonize a surface.

For this reason, you should make sure that there are no lights emitting UV light or near-UV light during the first 3-4 days of the first nitrogen cycle in your tank.

At all other times, you need not worry about keeping UV light or near-UV light away from your fish tank. Eventually, there will be fewer cells of nitrifying bacteria suspended within the water column, removing the need to be protective of them.

5. Test The Water

In order to make sure that you have a healthy population of nitrifying bacteria within your fish tank, it is recommended that you buy chemistry test kits for your aquarium.

Ammonia test kits are affordable and serve a critical purpose. At the beginning of the nitrogen cycle within a fish tank, the ammonia levels will increase rapidly. They will then plummet quickly as the nitrite-forming bacteria begin to take effect.

It may take a little bit for the nitrate-forming bacteria to bring nitrite levels under control since the nitrate-forming bacteria (Nitrobacter) don’t grow until there is enough nitrite present for them to consume.

All while this process is occurring, more ammonia is being released by the fish who are already present in the tank.

Testing Kits

You will be able to determine that the nitrogen cycle is occurring properly by purchasing test kits. When nitrate can be detected in your fish tanks, you will know that the nitrogen cycle is taking place, and you likely have a healthy population of bacteria within your tank.

You can start off by buying a simple nitrate test. Test kits for your aquarium are affordable and can be purchased online:

You can ensure proper care of your freshwater aquarium by buying complete test kits that measure more parameters than just nitrate.

Water API Testing Kit - Freshwater Nitrifying

One of the parameters you can test other than nitrate is ammonia. Testing ammonia can become necessary if your aquarium does not seem to be a healthy environment. High levels of ammonia in a tank that has been well established would indicate that the nitrogen cycle is not taking place.

You can find ammonia test kits such as the API Nitrate Test Kit and nitrite test kits such as this one as well.

You can find master test kits such as the one found here that include test strips for measuring all relevant parameters for freshwater aquariums.

When to Perform Tests on the Water in Your Fish Tank

Ammonia concentrations should be measured at least once a week, as is recommended in this article from the University of Florida. In an established tank, ammonia concentrations should not be at levels that can be detected by the test kits you buy online or at aquarium supply stores.

If ammonia is detected, possible causes include:

  • The bio-filter in your fish tank is not working
  • Your tank has not yet cycled

How Long Does The Nitrogen Cycle Take?

The nitrogen cycle can take anywhere from 2-6 weeks in a brand new freshwater fish tank. The amount of time it takes for a brand new fish tank to go through a nitrogen cycle the first time depends upon a variety of factors.

For one thing, it depends upon the amount of ammonia being produced during the cycle. This is why it is ideal to stock an aquarium with only a couple of fish at the start.

The time it takes for the first nitrogen cycle to take place also depends upon whether additives that provide habitat to bacteria are used.

6. Maintain An Optimal pH Range For Bacterial Growth

The acidity of the water of your fish tank will also have an impact on the growth of nitrifying bacteria. This is yet another thing you’ll have to test for.

The optimal pH range for Nitrosomonas is approximately 7.8-8, while the optimal pH range for the Nitrobacter bacteria is 7.3-7.5, according to this article.

At a pH below 6.5, nitrification will be effectively inhibited. Also, the ammonia in the water will be mildly toxic when the pH level is at 6.5, as most of the ammonia in the water will be in the ionized NH3+ state.

How Can I Measure The pH level of the water in my fish tank?

Water Testing Kit - Freshwater Nitrifying Bacteria
Picture: Water Testing Kit API Master – Freshwater Nitrifying Bacteria Grow

To measure the pH level of the water in your fish tank, you can buy test strips that will give you an approximate measure of the acidity of the water in the tank.

These pH test kits can be purchased separately from other test kits such as is the case with this box of pH test strips. They can also be bought as part of a master test kit for aquariums that will include test strips to measure other important water quality parameters.

How Can I Change The pH Level of The Water in my Fish Tank?

Factors influencing the pH level of the water in your fish tank are described in further detail here. I briefly touch base on how to maintain a balanced pH level in order to keep healthy bacteria in your fish tank.

Factors influencing pH level changes in your fish tank include:

  • The routine changing of water in the fish tank
  • A decrease in aeration will lower the pH of the fish tank
  • A high concentration of nitrate can also cause the pH level of a fish tank to lower

You can raise the pH level of the water in a fish tank very easily:

Add one (1) teaspoon of baking soda for every five (5) gallons of water that your fish tank holds. It is preferred that you remove the fish from the tank before doing this.

If you cannot remove the fish from your tank, make sure that you add no more than a teaspoon over the course of a day or so, as major changes can have a dramatic effect on the health of the fish.

You can lower the pH level of your fish tank by :

  • Decreasing the aeration in your fish tank
  • Adding peat moss within a mesh bag to the fish tank’s filter

7. Directly Add Nitrifying Solution to Boost the Process

This step is optional. You can buy a nitrifying solution to speed up the nitrogen cycle in your fish tank. This can be particularly helpful if you are having trouble getting your fish tank to cycle.

API Quick Start Nitrifying Bacteria contains live bacteria that you can add directly to your fish tank.

According to above mentioned article from Duke University, users of these quick-start bacteria solutions report mixed results. Some who use these products report success, while others claim that they do not work at all. Keep this in mind before you decide to go through with additional steps.

For such products to work, nitrifying bacteria need to have adequate access to oxygen and food. The effectiveness of these products depends on how long they’ve been on the shelf. If you do buy bottles of live bacteria to add to your fish tank, make sure that you are using it up quickly after buying it.

8. Speed Up The Nitrogen Cycle With Biomedia

This step is also optional. You can help speed up the nitrogen cycle within your freshwater aquarium by adding biomedia to you to the filter component or sump of your tank. There are mixed reviews about whether this works or not, but it’s a relatively inexpensive experiment if you want to try.

Biomedia act as a habitat space for beneficial microbes within an aquarium ecosystem. The nitrifying bacteria colonize the outside of the biomedia while the inside pores of the biomedia are inhabited by denitrifying bacteria.

A good example of a biomedia for your freshwater fish tank is the EcoBio-Stone – this amount can treat up to 80 gallon Fish Tank. The stone is made out of volcanic rock and cement and contains pores for denitrifying bacteria.

Adding one of these stones to your filter component or sump can help speed up the nitrogen cycle within your fish tank. Biomedia also helps to clear up and deodorize cloudy water. The stone contains calcium and trace minerals that are released into the aquarium.

Keep the Fish Tank Clean and Healthy

Keep your Fish Tank Clean
Picture: Keep your Fish Tank Clean

Properly maintaining an aquarium requires a watchful eye. If you step away from it for a while, the tiny ecosystem in your fish tank can spiral out of control. Watch also for algae or even consider getting so-called Algae Eaters – Fish to your fish tank.

One of the most critical components of a healthy fish tank is the nitrogen cycle. Fish excrete ammonia, which in turn can end up being toxic for the fish if concentrations increase rapidly. Fortunately, nitrifying bacteria will take up residence in a fish tank and break down harmful ammonia into less harmful forms.

The bacteria are everywhere – in the air and in the water. In the right conditions, colonies of nitrifying bacteria should be able to grow in the filter component or the sump of the fish tank.

You can always speed up the growth of colonies by purchasing a supply of live bacteria or some type of biomedia to give a home to colonies. Consider also Limestone, positive addition to your Fish Tank eco-system.

In the meantime, you have your checklist:

  • Select your filter/check what kind of filter you have
  • Introduce starter fish into the tank
  • Maintain the temperature of the water by heater
  • Keep UV light and near-UV light away
  • Perform necessary water chemistry tests
  • Maintain the pH level of the water in the tank
  • Ensure that there is phosphate in the water

Once your tank has an established population of bacteria, you should still take care to not clutter your tank. If you add too many fish at once, the amount of ammonia that is produced by the fish may easily exceed the capacity of the nitrifying bacteria to break down the ammonia into less toxic forms.

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How to Grow Good Bacteria in a Fish Tank - 8 Steps