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Duckweed | Home Fish Aquarium Guide

Home Fish Aquarium Guide

Fishkeeping Information and Resources for the Home Aquarium

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It’s funny how so many things can be a nightmare, or a God-send…. Duckweed is one of those things. For many people they absolutely HATE it. It multiplies quickly and can cover the surface of a tank. It can be hard to get rid of. I’ve seen some people say that they scoop cups of it out every day and still haven’t gotten rid of it.

If the conditions are right it will absolutely take over the surface of your tank. Now it will usually have between 1-4 tiny leaves floating on the surface as somewhat of a lily pad arrangement. There will be about an inch worth of root hanging down below. (*This can be a good hideout for fish fry and a good place for baby fish feeding on little critters that may hang around that cover.)

It’s good for removing nitrates from the tank. It reproduces via vegetative propagation. Baby plants grow from leaves on the parent plant and then float free.

Since here we’re focused on the pest aspect of this plant….

Eradication can be a challenge. One of the best ways is to not let it into a tank. I first got some duckweed as a tag along on some plants from my local fish store. There were about a half a dozen of the plantlets. Then after about 2 weeks I had 2 dozen or more (*maybe 3 dozen.) I suspect in another month it will have taken over the tank surface. The bad side of taking over the surface is that it will shade out my other plants, some of which would like to have a bit of light. 😉

So, how do you remove them once they’re established? Scoop them out. Scoop them out and scoop them out some more. Day in, day out. You may never get every last one of them, but keep scooping to keep them at least under control. There are some fish that will eat duckweed, (koi, goldfish). Of course, those are cold water fish and probably not suitable for a community tropical tank. As a side note, I do see cups of duckweed going on ebay from $3 with $5 shipping for a 4×4 inch surface area up to $6 a cup with $8 shipping…. don’t know how many buyers there are, but, who knows maybe you could make a bit of money off of this prolific pest. (At least that way you’ve got some reason to tolerate a bit of it surviving in your tank.

Another aspect of control of duckweed may be control excess ammonia/nitrates in the tank. If the water parameters are in balance it may not reproduce as prolifically.

Some fish will eat Duckweed (goldfish for instance.) I don’t know which other varieties will snack on it. It does stick to your arms when you reach into the tank and one or two pieces don’t seem to do much harm. Once it reaches a critical mass number wise it seems to explode. (Should be a good thing if you’re trying to control ammonia/nitrates.)

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February 4, 2011 - 11:02 PM