Phytoplankton Culture: A Guide to Growing Phytoplankton at Home

In the ocean, fish and invertebrates have access to nature’s bounty and dine at the best buffet line ever created.

Aquarium food tends to be much less interesting.

One thing you can do to liven up the food chain in your aquarium is to culture phytoplankton at home.

Phytoplankton are one of the basic building blocks in the food chain It can be fed to corals and clams or be used as a nutrition-packed food for other live foods like rotifers, copepods or brine shrimp. Loading up the guts of these other live foods with nutrient-rich phytoplankton is a technique used by aquaculture houses called gut-loading (literally loading their guy with phytoplankton). When your fish or inverts eat those live foods now, they get the brine shrimp and the phytoplankton in the brine shrimp’s gut.

If you are interested in breeding saltwater fish, you will need to master the art of phytoplankton culture–so that you can feed the tiny fry that are born.

Here is how I established a phytoplankton culture when I was breeding saltwater fish:

Phytoplankton Culture: Equipment List

Feel free to customize this list based on what you have available to you. For example, you could use a 48-inch fluorescent tube shop light instead of an LED light (that’s what I used years ago…before LED lights were this inexpensive). A lot of people also use empty soda bottles instead of gallon jugs. It all depends on how many bottles you want to start and how much phyto you want to grow.

At one point in time, I had 7 x 2L bottles running with my phytoplankton culture. I found working with a few, larger containers to be the right tradeoff of time/maintenance required.

Where to get your equipment

You could get most of this equipment at your local pet store, hardware store or online at

Phytoplankton and rotifer cultures

How to set up your phytoplankton culture equipment

  • Mount the LED light horizontally on a wall just slightly above table-height
  • Slide the table up against the wall, just under the light
  • Spread your culture bottles out along the length of the LED light to give each bottle maximum exposure to the light output
  • Cut 3 pieces of rigid tubing to be at least 12 inches high. You want it to be long enough to reach the bottom of your culture bottle and still extend over the top of the container
  • Measure how far away the splitter will be from each of the culture bottles and cut 3 pieces of flexible air tubing long enough to reach from the top of the rigid tube over to the airline splitter
  • Measure how far away the splitter will be from the air pump and cut 1 piece of flexible airline tubing long enough to reach from the air pump to the input side of the splitter
  • Attach flexible tubing from air pump to splitter
  • Attach 3 pieces of flexible airline tubing to 3 open ports on the airline splitter
  • Attach the other end of the airline tubing to each of the 3 lengths of rigid tubing
  • Insert rigid tubing into culture bottle
  • Turn on the air pump
  • Fill bottles with a small amount of freshwater to test and make sure all 3 airlines create a modest flow of bubbles. Adjust flow rate on the splitter as necessary to create uniform moderate flow

This is what my set-up looks like

phytoplankton culture set up for growing phytoplankton at home

This is what my phytoplankton culture set up looks like in my basement

The image above shows what my phytoplankton culture setup looks like. I have a 48-inch fluorescent shop light mounted horizontally, behind the table and three culture containers–two 1 gallon jugs and 1 32-ounce jug. When I first started, I had more 2-L soda bottles, but I found that the 1-gallon size, for me, was the right blend of volume and maintenance that I was looking for.

Making the Phytoplankton Culture Media Before Starter Culture Arrives

In order to grow your phytoplankton, you want to create what we will call the culture media. The culture media is the saltwater solution that the plankton will grow in. What you are aiming for here is to create the ideal conditions for rapid growth.

As mentioned before, I grow Nannochloropsis occulata, which is a phytoplankton that prefers relatively dilute saltwater and fertilizer.

Here is how you make the phytoplankton culture media:

  • Slowly add aquarium salt mix to freshwater to create a gallon of the saltwater solution with a specific gravity of 1.014.  Remember, this is less salty than full-strength aquarium water.
  • Stir the water, then add the fertilizer according to the label–if using Micro Algae Grow, from Florida Aqua Farms, then add 40 drops per gallon.
  • Let the water ‘age’ overnight before using this water officially in your culture. To allow time for you to safely ‘age’ your water, please do this step at least a day before your starter culture arrives.

Starting the Culture—What to Do Once Your Starter Culture Arrives

Once your starter culture arrives and you are ready to start growing phytoplankton at home, you can start by:

  • Carefully pouring your starter culture into a clean water jug
  • Add enough media to the culture to double the volume in the jug. (eg. if you have 500 mL culture, add 500 mL of media)

A few notes/commentary here: if you are starting out with a small culture, you may want to start with a small/narrow container so that you can give the culture proper illumination from the side. The more volume you have, the more phytoplankton you can and will eventually grow, so you are trying to increase the culture to fill the containers, but you want to do so gradually so that you don’t shock and kill the culture.

  • Insert a rigid airline into the culture jug and start a moderate flow of bubbles.

Watch the culture over the next few days.  Doubling the volume of water in the culture should turn the color from a relatively darker green into a relatively lighter green.

Once the culture returns to the original shade of green, double the volume again one more time and repeat this process until you completely fill your culture jug. (to continue the example we started before, you would add 1000 mL of media to the 1000mL culture and then fill it to almost the top a few days later when the culture is dark green again—at that point, you should have a 1-gallon culture of phytoplankton)

You will also need to make another batch of culture media. This time, you will need 2 more gallons of media.

Grow-out and Harvest

Once you have filled your first container, the is up and running. Now your goal is to start the culture running in a few more bottles. After a few days, when your 1-gallon culture bottle starts to turn dark green, you want to separate that culture:

  • Pour 1/3 of the culture into 2 new bottles, so that there is 1/3 gallon in each of the three bottles now
  • Top them off with fresh media, set them in front of the light and get ready to harvest in a week.  From then on out, harvest 2/3 of each bottle, keep the remaining 1/3 in the original bottle and top-off with new (aged) media.
  • Place rigid airlines in all 3 containers and ensure each culture bottle has moderate bubbling and good exposure to the light

You want to be careful when removing the rigid airline from the phytoplankton culture. One of the biggest risks you face is contaminating your culture and causing a culture crash. You will want to sterilize the areas before you put the tubes down and try to minimize contact with unclean surfaces.

Harvesting Phytoplankton

You harvest the phytoplankton by removing 1/2 to 2/3 of the culture from the growing container, once the color grows dark—which should be about once a week—although you will want to watch your own culture and adjust that timing based on when it is at or just before peak coloration—peak coloration essentially means the concentration of phytoplankton is optimal/peak density.

Simply pour out 2/3 of the culture into a storage container (or package into smaller bottles) and refill the volume with new (aged) culture media.

A quick post here to think about—do you want or need a continuous source of the freshest phytoplankton or do you want to minimize the time you spend doing all the phytoplankton culture chores?

Your answer to the question will provide you an opportunity to tweak the methods described here to best suit your own needs.

As I described it here, your phytoplankton culture will yield ~2 gallons of dense culture about every 7 days or so (depending on the intensity of the light, bubbling, culture growth, etc.). If you can’t use or store that much, you may want to scale back and use smaller bottles and/or stagger the harvest days.

Rather than harvesting 2/3 of the volume every 7 days, stagger things on your first harvest so that one container is harvested 2/3, one by 1/2, and one by 1/3. The container that was only 1/3 harvested will ‘green-up’ first in a few days, followed by the 1/2 container, followed by the 1/3 container.

Once they green up, harvest an equal amount every time (go back to 2/3 for all containers) and your containers will be mature/ready for harvest on different days of the week. That will optimize your process for freshness.

Phytoplankton Culture Storage

Try to use some of your fresh phytoplankton right away. If you did grow more than you can use, storing your phytoplankton is easy.

Simply fill and cap empty water bottles and keep it in the refrigerator.

phytoplankton culture bottles for storing nannochloropsis

I use these reusable water bottles to store my phytoplankton after harvest

If storing the phytoplankton for longer periods of time, you’ll notice that the phytoplankton cells settle to the bottom–make sure you shake it up at least once a week or the culture will spoil/rot.

Look for any off smells from your phytoplankton and dispose of older, saved material if you detect strong ammonia. Don’t take any chances there, it’s not worth it.

Here is an important, real-life tip: if you are using a food refrigerator, be sure to keep things separate from food items. You don’t want to cause contamination or make anyone sick. Also be sure to label it very explicitly.

A family member was over our house one day, didn’t know that the water bottles in the bottom of the fridge were filled with rotifers (not phytoplankton) and they drank it. Yes, they drank it. Gross.

They didn’t get sick, they spit it out right away (tasted terrible) but hopefully you get the message. Don’t be a dope, like me.

Dosing Phytoplankton

Here is more information about how to dose phytoplankton in your reef tank

Join the Community!

It's easy to join. Get a FREE book and newsletter!

Join Now

Written by Albert B. Ulrich III. Follow me on Google + and Twitter