How to Culture Phytoplankton

How to Culture Phytoplankton

In order to keep your aquarium fish and invertebrates active, healthy, and well-nourished — you need to feed them adequately with a nutrient-rich diet. Though there are many food items that you can serve your fish and inverts, most of them are relatively expensive. Hence, growing a few ones indoors (like phytoplankton) can save you a great deal of money.

From the variety of food sources available, phytoplankton — a single-celled organism and autotroph — is unarguably one of the easiest, cost-effective, highly nutritional, and widely used aquarium food.

Of course, the best option here would be to culture your own phytoplankton. As a result, you can steadily feed your tank inhabitants with— rather than opting for the alternative route which is buying live phytoplankton regularly from local fish stores.

Keep reading for more information on how to culture phytoplankton for use in your home aquarium.

What is Phytoplankton?

Phytoplankton are microscopic, single-celled organisms that inhabit aquatic environments (freshwater and saltwater) which provide ideal conditions for its growth and multiplication.

Phytoplankton usually inhabit a well-lit surface layer or euphotic zone of a sea, lake, ocean, and other bodies of water. The three important groups of phytoplankton are:

these organisms form the base of freshwater and marine food webs.

Furthermore, phytoplankton is a primary producer or autotroph — an organism capable of producing its own food using the sun’s energy to convert inorganic molecules like carbon dioxide into energy-rich organic compounds and oxygen.

Essentially, phytoplankton will provide nutrition for themselves through synthesis of their cellular constituents in the presence of light energy. So, the process by which this food production is carried out is called photosynthesis.

In the aquarium hobby, few species of phytoplankton are cultured to cater for the feeding needs of micro fauna — rotifers, copepods, daphnia, brine shrimp, as well as other captive invertebrates.

Such species include the renowned and most commonly used Nannochloropsis oculata, as well as others like Isochrysis galbana, and Tetraselmis spp. For home phytoplankton culturing, we will explain what you need and how to achieve this in the subsequent sections.

Equipment You Will Need to Culture Phytoplankton

How to Culture Phytoplankton - Basic DIY SetupTo culture fresh phytoplankton for your aquarium, you will need the following materials (links to check the price on Amazon):

How to Culture Phytoplankton algorithmSetting It Up

  1. First, you have to get the culture container or vessel(s) ready by sterilizing it with vinegar and water or rubbing alcohol to prevent contamination.
  2. Afterward, drill two holes in the cap of each culture vessel, one to connect the airline tubing to the air pump and another to promote the exchange of gases.
    Note: If we leave the bottle open, there will be a higher risk of water contamination. We do not want anything to get there! That is why it is recommended to keep the cap.
  3. Cut the rigid airline tubing a bit more than the total length of the container, then insert it down to the base of the container/bottle making sure that the rigid airline tubing goes through the bottle’s cap. Bend the rigid airline tubing slightly at the upper level to form a curved or “U” shape.
    Note: Don’t jam the rigid airline tubing against the bottom.
  4. Join the rigid airline tubing to the flexible airline tubing, then connect it to an air pump to provide adequate flow to the culture throughout the culture period.
    The bubbles should be strong enough to stir up the whole container (not too aggressive not too weak).
    If you have multiple bottles, connect all tubing to an airline splitter, and extend it to the air pump. When you are done, keep the tubing and the air pump aside, and proceed with the remaining steps.
    Important: Do not use an air stone because it will create microbubbles and simply skim your phytoplankton.
  5. Note: Make sure to install a check valve to bridge the airline tubing if your air pump is below your culture. This helps prevent water flow return, especially during a power outage as such occurrence can damage the air pump. An airflow adjuster is also required to permit regulation of the flow rate — the amount of flow which the culture vessel receives.

Creating the Culture Media

Now, it’s time to create the culture media. Basically, culture media is a mixture of saltwater solution and growth fertilizer.

  1. To achieve this, pour a quality sea salt mix into 2 liters of RO/DI freshwater and make sure to attain specific gravity of 1.019 – 026for best results. Measure this with a good refractometer. Do not go just by measurements or weight when mixing saltwater.

Note: pH should be more than 8.0 – ideally 8.2.
Important: Never use old water from your tank! It always has to be nice freshly mixed saltwater.

  1. Next, pour the saltwater solution into the containers and add the whole disk of live phytoplankton; that’s for the coagulated type from Florida aqua farms.
    An alternative is the liquid starter culture available in local fish stores, purchase this and empty the whole 500 ml (or 16 oz) can into the culture container. Do not overfill the container, leave a little space to serve as an air gap instead.
  2. Afterward, shake the bottle of F/2 medium fertilizer (Guillard’s, 

Micro Algae Grow ™, etc.). Measure 2 – 4 ml (0.06 – 0.12 oz) of fertilizer per 4 liters (135 oz). Use a measuring syringe or pipette and add to the solution.
However, if there is a specific dosage indicated in the product’s package, you can follow that instead.


How to Culture Phytoplankton many bottlesMake a decision on where to place your culture containers. Is it on a shelf in your room? Inside a big bucket in your kitchen/room, on a table or kitchen counter? The objective is to place the culture vessel (s) where it will remain undisturbed during the entire process.

  • Well, if you are using a shelf — mount the light towards the rear, then arrange the culture containers in front of the light source to maximize exposure.
  • Insert the rigid tubing back into the culture vessels and turn on the air pump.
  • Also, keep a little distance between the vessels, and if you have a clip-on grow light as opposed to a LED light bar, place it not farther than 6 – 8 inches (15 – 20 cm) away from the culture vessels.
  • Be sure to connect the light to a timer, and set a minimum of 16:8 (hours) light/dark cycle every day.
  • Do not place your culture containers on the window, direct sunlight will overheat and kill the culture.
  • Lastly, turn on the air pump and adjust the flow rate to supply moderate yet ample air bubbles to the culture.

Safety Tips

Clean the airline tubing properly from time to time, and sterilize the culture bottles to minimize the risk of contamination.

Exposure of the culture equipment to bacteria and other contaminants may trigger a massive crash or die-off of the phytoplankton cells. To this end, you are to clean/sterilize the culture vessels and other materials before usage/ after a series of usage.

Things to Note

In the cultivation of phytoplankton as an aqua-feed, you need to be aware of the factors that can influence its growth and survival.

1.     Lighting:

The essence of artificial illumination is to provide an energy source that facilitates photosynthesis— making it possible for minute algae cells to grow and proliferate within the culture vessel.

Therefore, you should maintain a minimum of 16:8 hours light/darkness daily. I know that some aquarists even tend to leave the light on for complete 24 hours without any noticeable issue.

The opacity of the culture vessel will influence the amount of that light that penetrates through it. Hence a clear, plastic container is clearly a good choice for culturing phytoplankton.

2.     Temperature:

Phytoplankton may not grow well in extreme temperature conditions, but as for Nannochloropsis oculata, it will thrive under room temperature.

Temperature control is a walk-through since you do not need a heater or chiller present to be able to culture phytoplankton in your home, standard room temperature about 20 °C (68 °F) is adequate. You don’t want it too hot or too cold.

3.     Flow:

The presence of bubbling movement (aeration) in the culture vessel will help distribute the nutrients and microalgae cells all over the container. Also, it will facilitate the exchange of gases which avails the phytoplankton to remain in good condition.

Importantly, it encourages even distribution of essential nutrients, maintains the pH levels, and promotes rapid growth/multiplication of the phytoplankton cells. That’s why you need an air pump for your culture.

Note: If you noticed that the culture looks a little lighter on the second day that’s because a lot of the phytoplankton has settled to the bottom. You can stir it up with a spoon and/or increase the flow a little bit. Do not let it stay on the bottom because it can suffocate and die.

4.     Fertilization:

The culture media typically consists of saltwater enriched with nutrients via application of a Guillard’s F/2 medium fertilizer such as the Micro Algae Grow™ and Reefphyto Phytoplankton Nutrient in the right dosage.

This fertilizer contains adequate amounts of nitrates, phosphates, and other essential nutrients that will support high algal yields.

Harvesting the Phytoplankton Culture

How to Culture Phytoplankton - harvestingThe algal biomass in the culture vessel will attain a high density (indicated by a dark green color) after some days — usually between 5 – 7 days.

Under favorable conditions, the cell divides up to 8 times a day. As it grows (7-17 days), phytoplankton enters a “balance” phase between the number of phyto cells, the availability of nutrients, free space, and other conditions.

Note: Keep in mind that the culture may crash after this period as its population continues to increase massively.

The “extinction” phase starts on the 17-25th day. You will see that the cells begin to die and settle down to the bottom of the container.

Now, you can proceed to harvest about ½ or ⅔ of your grown phytoplankton culture in a separate, clean container.

Then, add freshly prepared culture media to the remaining culture and allow it to keep growing. The remaining culture serves as the inoculant.

You can keep on repeating this process to produce new batches of phytoplankton. Just don’t forget to add fertilizer!

Storing The Phytoplankton Culture

Harvested phytoplankton culture should be properly canned and stored in a refrigerator pending usage. DO NOT put it into a freezer!

Also, be sure to shake the bottles every day to prevent the phytoplankton cells from settling at the bottom, since that can cause it to go bad.

This way it can be easily stored for at least 3 months.

In Conclusion

Culturing phytoplankton is a great and effective way to minimize the high costs involved in feeding aquarium fauna.

Phytoplankton is quite easy to culture once specific conditions such as lighting, aeration, nutrition, and salinity are sufficiently present to support its growth.

By far, the overall cost of culturing phytoplankton is minimal when compared to a lot of other feeding options. Ultimately, even beginner hobbyists can be able to grow a substantial mass of fresh phytoplankton for their tanks.

Related articles:

Green Water Algae Profile and How to Remove

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