Daphnia are small aquatic crustaceans also known as water fleas.
In the aquarium hobby they can be an easy replenishable source of fish food. I find daphnia can be good for small nano fish (although some adult daphnia may be a bit big) all the way up to about Betta fish size.
They live in fresh water, so any daphnia that don't get eaten right away may live for a bit for a future snack.
I have been growing daphnia for about a year in a couple different ways. Below I’ll go through what I found in my research and what I have found from my personal experience.
So how do you take care of daphnia?
All you really need is water, light, and some starter daphnia.
Water
Dechlorinated water. Use aged water and fish tank water.
My experience:
Dechlorinated water. I also used some fish tank water that didn’t have high nitrates. Most of my water refills outside is through rain water, so you don’t need aged water. For the tank, larger volume is easier, but I think more importantly is surface area. I have kept daphnia in glass cylinders, 5 gallon buckets, plastic storage container, and a plastic quarter barrel container. Best success were the plastic storage container and quarter barrel with the large surface areas. You can have them in the other ones but I was having trouble with them.
Light
Not too much is said about lights
My experience:
Daphnia seem attracted to light. Light will also grow their food. I have a desk lamp on for about 10 hours a day and that works for me. I have also read a recommendation to have light 24x7. I think that might be costing more than it is worth.
Daphnia
The daphnia need to come from somewhere. I recommend starting with live daphnia instead of buying eggs. I have gone the eggs route and have had some hatch, but when trying to hatch a second batch, I didn't get any to hatch. My current culture I got online shipped to me live. There are a couple types of daphnia. I believe the care is the same whichever one you get.
Food
Daphnia are filter feeders, they eat very small things floating in the water. There are a variety of things to feed the daphnia. I won’t go into all the different ways to feed them.
My experience:
What I personally try is for my daphnia inside, green water (water that has turned green with the free floating algae) and powdered spirulina. I have a small patio pond (guessing around 20 gallons) outside and I do not feed it. The daphnia feed on whatever grows in there and the tank so far is quite clear. I actually don't feed my smaller indoor daphnia culture much anymore and rely mostly on what grows in the water from the lights. There aren't a huge amount of daphnia but there is a steady amount.
Temperature
I have read and seen a variety amount of temperatures. In my experience, room temperature is fine. In fact in the pond outside, I was seeing daphnia out at 40 degrees! Your culture can survive the winter in the NOVA area
They may lay eggs and die off during the freeze (can't collect them anyways because the water is frozen), but they will hatch and come back very shortly after the water thaws and the sun starts to steadily shine again.
Water circulation
I have read things from you need an airstone to you need an actual filter in the tank
My experience:
You don't need either. In my tub outside I don't run anything but I run an airstone inside that doesn't circulate the water but disrupts the water surface. My goal there is not to move the water around but to discourage mosquitoes from laying in there. When the weather gets warmer I most likely will need to do something to my pond outside to prevent mosquitoes there too.
Harvesting
Harvest often. Baby daphnia are very small. To collect them you will need a fairly fine net. At a certain tank size, you almost can't harvest too much as there are so many. You also will want to harvest enough to prevent overcrowding which can lead to crashes in the daphnia colony.
Daphnia can be a very easy way to raise you own live fish food. I am easily raising a lot outside without any feedings or water changes and just using the sun for light.
