Daphnia Culturing – How to Raise Daphnia

How would you like to cultivate and raise your own separate tank of Daphnia (also known as water fleas)? These tiny plankton-like freshwater crustaceans grow to about 3 millimeters in length or less. They’re actually kind of cute looking as you watch them swim almost vertically in their tank. They live quite happily in large groups within a tank, so that you can harvest them when you need them to feed your fish, tadpoles, salamanders, newts, or aquatic insects.

In this article, we’ll discuss everything you need to know about these teeny Daphnia, so that you can have a successful, fresh, and continuous food supply!

Setting up a Daphnia Tank

Daphnia are freshwater creatures that can be kept in a tank as small as 5 or 6 gallons and all the way up to 360 gallons! The main thing to look for in a tank is a greater surface area than depth. That helps mimic their natural environment of ponds and other freshwater habitats. A store sized 360-gallon tank used to cultivate thousands of Daphnia for hundreds of fish measures six feet long, four feet wide, and only two feet tall. So, for smaller tanks, find ones that aren’t very deep.

It's not just putting together a tank, but an ecosystem for Daphnia. Freshwater plants like duckweed, shrimps or snails, and algae help them thrive. Daphnia also keep the water clean, just like saltwater shrimp, although if you have thousands of Daphnia, they can make the water look much cloudier than it actually is. They far prefer living at the top of the surface of the water, especially the babies and juveniles. 

As for water temperature, you want to keep it around 68 degrees Fahrenheit (20 degrees Celsius). Freshwater plants like duckweed can be added, too. To boost the mineral and electrolyte content, a Wonder Shell makes a big difference. It adds hardness to the water and is also a dechlorinator.

Chlorine kills Daphnia, so make sure you properly condition your water first. Change the water at least once a month and take half of the water out of your tank and replace it with fresh water that’s been dechlorinated. It’s great to add used fresh fish water from another tank or water from your own pond. Aged water is better.

Daphnia are photosensitive so it helps to have a light on your tank running 24/7. The Daphnia will be drawn to the light.

Indoor Tank or Outdoor Tank?

Where you physically place your tank is important. While some Daphnia owners keep theirs outdoors, it’s best to bring the tank inside due to the following reasons:

• Temperature – there are fewer temperature fluctuations indoors.
• No mosquito larvae – any mosquito eggs that aren’t eaten by the Daphnia turn into larvae, which turn into mosquitos.
• Prevent invasive species – you won’t have problems with other species like Copepods (“Cyclops”) in an indoor tank.

Tank Aeration

What about aeration? This is a popular and confusing topic when it comes to keeping Daphnia, and there’s a lot of conflicting information. Aeration will give you a higher yield, so it is recommended. Daphnia seem to really thrive with a coarse air stone, especially one that’s weighted so they don’t sink. The medium sized bubbles can be at a pretty rapid ‘rolling boil’ consistency. When you position the aeration at one end of the tank, the Daphnia can swim to the other end if they want calmer water. Standard airline tubing will help keep the water flowing. Aeration is much preferred over stagnant water. This makes sense because, in the wild, Daphnia living in a pond or stream would thrive well in moving water. It really helps your yields grow.

Aeration also solves another issue – keeping freshwater plants like duckweed from taking over. The constant bubbles can clear a space.

Shrimp and Snails

Daphnia and duckweed aren’t the only living things to have in your tank. Especially if you have a very large tank with Daphnia, it helps to have more debris feeders like freshwater shrimp and snails. Buy ones that won’t prey on the Daphnia. They will clean up the bottom of the tanks, eating extra yeast and other microscopic particles.

Busting Daphnia Tank Myths!

Along with setting up your Daphnia tank, there are some myths you might have heard about or read that simply aren’t true. Let’s go through them one by one:

#1 – Green Water Doesn’t Matter

You don’t need green water or to start with green water for Daphnia. Daphnia are such great water cleaners that they can clean up lots of gallons in a matter of two days. So, don’t be afraid to add lots of food yeast and spirulina. They will eat a lot! The smaller the tank, the less green water you will see because the Daphnia clean it up so fast.

#2 – Daphnia Reproduce Every 8 Days

Daphnia are really good at exponential math. It only takes eight days for a baby Daphnia to grow to maturity and begin breeding. Each Daphnia has ten babies. If you have 100 Daphnia today, you’ll have 1000 Daphnia in a week. A week after that, you’ll have 10,000 Daphnia. And so on! In a month, you could go from 100 Daphnia to 100,000 Daphnia. Their life cycle is only a couple of months.

#3 – Don’t Underestimate Food Amounts

Along with #2 above, your Daphnia population is skyrocketing. So, don’t underestimate how much they’re eating and how fast they grow and reproduce. Even when you do daily harvesting, that’s still some serious breeding population numbers to deal with.

#4 – Handling the Daphnia Population Crash

Since Daphnia breed so rapidly and in such large numbers, you could have population crashes. This is especially true for smaller tanks. More water can handle more waste from the Daphnia, so bigger tanks are better. You would probably want at least a 55-gallon tank.

What do I Feed Daphnia?

In their natural pond habitats, Daphnia feed on algae, bacterial flora, and other tiny plankton creatures even smaller than themselves. In your tank, though, you will feed them active dry yeast. Yes, this is the same stuff used to make bread! It is a type of cake yeast that is still in a semi-dormant state. Combine the yeast with a bit of water to activate the cultures. You might want to use an immersion blender rather than mixing by hand. Your Daphnia food is now ready.

You can also add spirulina powder to your Daphnia tank. It’s an algae super food that turns the water green, too.

How often should you feed Daphnia? That depends on the state of the water in your tank. Once the water is clear, that’s when it’s time to feed. Sprinkle the yeast mixture on the surface. The Daphnia become very active at feeding times.

Daphnia will also eat algae, so you can cultivate some of these green plants along the sides of the tanks.

How to Harvest Daphnia

It’s a simple and easy process to harvest your live Daphnia from your tank to feed your fish and other aquatic animals. All you will need is a handled fine mesh aquarium strainer net and a container to put the Daphnia in.

Gently scoop the strainer through the high-density Daphnia at the water surface to get as much as you can. These Daphnia are a light brown in color, so you will see a lot of them in the bottom of the net. Gently lift the net from the tank and shake it to remove the rest of the water. Only scoop through a few times, and don’t make your movements too fast or ‘swishy.’ That will drudge up the debris from the bottom of the tank. Stick to the surface of the tank.

You can get a surprisingly large amount of Daphnia after just a few light scoops. They’re so tiny. Once you’ve harvested your Daphnia, you can transfer them directly to the fish tank for feeding or put them in a tiny water jar for fish feeding within the hour or so.

Harvest a lot! You won’t decimate a population by harvesting as much as you want. They will just reproduce rapidly. In fact, harvesting frequently helps prevent crashes and makes life better for the existing Daphnia.