Duckweed (Lemnaceae), also known as water lens and bayroot, is a tiny floating plant, that holds the distinction of being one of the smallest flowering plants in existence.
It can be found in nearly every type of aquatic environment, but only truly thrives and proliferates in environments that have little in the way of current. In wetlands and ponds, where the water is almost completely still, duckweed can quickly overrun the entire surface of the pond. If it is allowed to completely cover the surface of the water, it can lead to oxygen deprivation, and may lead to large-scale fish die-offs.
Duckweed will thrive in nearly any aquarium, and in most cases will experience explosive growth thanks to the fertile environment that aquariums offer. Because of their impressive growth rate, they act as one of the best water purifiers that you can find for a fish tank and can be invaluable to newly established aquariums that are having water quality problems.
And if cleaning and purifying your aquarium’s water isn’t enough, they also have a well deserved reputation for reducing algae growth. Between the reduced light reaching the aquarium water, and the quick uptake of nutrients, any tank containing duckweed in anything approaching significant numbers will experience greatly reduced algae growth.
Of course everything comes with a downside, and once you have duckweed in a tank, it is almost impossible to ever completely remove it. It also has the annoying habit of clinging to everything that it touches, and anything that you remove from your aquarium, will end up looking like it’s covered with a forest of duckweed.
Care
Duckweed doesn’t require any special care, and will thrive in everything from low light to high light, and soft water to hard water conditions. It’s actually more difficult to get the duckweed not to grow, than it is to just sit back and allow it to grow on it’s own.
If you are looking for heavy growth, then provide it with a high quality, full spectrum light, with trace minerals adding during the weekly water change. The one that I personally add after every water change is Seachem Flourish Trace Elements
Reproduction
Duckweed mostly reproduces through asexual budding, but in rare cases it may also reproduce sexually. Its reproduction doesn’t require any intervention from the aquarist, and if the conditions are right, it will reproduce on its own.
Compatibility
Duckweed is compatible with most small fish, but will be hungrily devoured by herbivore fish and some cichlids. And that’s not necessarily a bad thing, since it is packed with nutrients and protein, and can even be used as a primary food source for some fish like goldfish and tilapia.
Of course if you want to cultivate duckweed, it should only be kept in tanks with smaller, non-herbivorous fish and even these may occasional eat small amounts. The fish that should be avoided are large cichlids, goldfish, ameca splendens and common plecos.
Is duckweed widely available at chain pet stores or should I just purchase online?
Most pet stores have it these days. Often they will have without even really want it. Often, if you have a local pet store, they will give it away for free, since it has a habit of finding its way into fish tanks and is hard to eradicate.
I have not seen it for sale in any stores but I have seen it in many stores’ aquatic plant tanks. Many employees are willing to include some ‘complementary’ duckweed if you ask while purchasing other plants from the tank.
DO guppies control it?
Unfortunately, guppies are too small to control duckweed. They may pick at it a bit, but with their small mouths and bodies, they won’t do much to stop the growth of duckweed.
What type of fish would you suggest to put in the tank with it? I teach ecosystems and am using this in my classroom tank this year and the years to come. I would like to keep fish inside due to food changes and being a mini “ecosystem”
A great, self-sustaining fish is the fathead minnow, also known as the rosy red minnow. They are very cheap and are often sold as bait minnows or feeder minnows at fish stores. They don’t require a heater and will often breed in aquariums, which I think would be great to watch for kids. They’re also incredibly hardy and very difficult to kill. Though the one downside is that it can sometimes be difficult to find healthy fish.
Another excellent fish would be guppies. These little fish breed regularly which would be fun to watch and as long as you stick with more of the regular guppies (not the fancy show ones), they’ll be pretty hardy.
A third option would be white cloud mountain minnows. These fish do well in unheated aquariums, are quite hardy, and also breed pretty easily in an aquarium. Plus, they were once known as the poor-man’s neon tetra for their vibrant colors.
I think any of these three fish would make great additions to the tank, though I tend to favour the fathead minnows, since they are native to North America and are highly underrated.
How much duckweed should you introduce in the beginning? Should I start with 5 plants? 10 plants? Do you have a guideline based on tank size?
Assuming you don’t have large fish, only a handful of duckweed will quickly colonize an aquarium. The problem is that many large fish love to eat duckweed, so if you’re placing it in a tank with a hungry fish, it might all get eaten quickly. Most stores sells duckweed in containers about the size of a coffee mug and if you place that many in the tank, it should take off pretty quickly. But be careful – once you put duckweed in a tank, it’s almost impossible to get it out again. It grows ridiculously fast.
Is Duckweed a good, main food source for White Cloud Mountain Minnows?
While they’ll eat it, it’s not a main food source. I would still stick with a high quality prepared food.
most garden centers with and aquatic section have it too
Is it better to let the duckweed form a carpet or should I remove sections of it so it doesnt choke itself out?
I should add this is only concerning the health of the duckweed, not the entire tank.
It’s best to keep an area at the top open, to keep the oxygen exchange going smoothly. Generally, the fish should disturb and eat enough of it that it shouldn’t be too much of a problem.
I have a tank with a beta and guppies are betas compatible with duck weed
Yes, duckweed is absolutely fine to keep with a betta. But just to be warned, bettas generally don’t like male guppies.
Do you know of any good filters that would be compatible with the duckweed?
Sponges filters are great with duckweed. I’ve also used hang-on-back filters in the past. The key to getting it to work with a hang-on-back filter is to limit the filter outflow on the top of the aquarium. I used clear tubing and suction cuts to create a safe and calm area for the duckweed to grow. It was very effective and allowed the duckweed to grow well–if that’s what you’re looking for of course.