Not a weird question at all. Collecting plants from ponds and streams can be a lot of fun. you can also introduce unwanted snails and other parasites unintentionally. There are a couple of ways to disinfect plants, but with floating plants that can be a little more challenging. One method is potassium permangenate. That can be difficult to get hold of and, from personal experience, does not kill snail eggs well. The other common option is to make a bleach dip. Some people use a 5% bleach, others 10% bleach. Here is a pretty good reference link: Jake’s Planted Aquarium Pages | Disinfecting Plants – Before or After
Some plants are bleach-sensitive, so I'd say use two small containers (I use 1-quart plastic wonton soup containers form my local Chinese restaurant!). Separate your Duckweed
into two groups. One group, do a bleach dip, submerging the Duckweed
by using a paper towel or rag. Remove the now-bleached Duckweed
, put it into a plastic container, fill with clean water and add a good amount of dechorinator. Let stand, mixing gently. Drain and replace with some dechlorinated water. Put the now-treated Duckweed
and untreated container of Duckweed
into a spot where it gets some light and wait a few days. If it doesn't die, treat the other bunch and add to your tank!
Keep an eye on both treated and untreated containers for snails or other things you might not want in your tank!