Wild Duckweed

[Epiphanaea]

My goldfish love duckweed (of course). I’ve bought from a lfs but they don’t grow it in sufficient quantity and they’re a 45 minute drive away anyway.  I ordered some online but it was expensive, contained a lot of dead leaves, and also contained scuds - which got me thinking about whether store-bought was actually any more sanitary than foraged.  
 

There is a section of an old canal lock in a nearby park that is completely carpeted with duckweed.  I’ve seen people fishing on the canal so harvesting some duckweed would presumably be acceptable too.  
 

If I rinsed it very well in vinegar, then water, and then floated it in a bowl in water treated with anti-parasitic medication for a few days, then rinsed again, do you think this would be safe (or no less safe as ordering it online)?  Not good enough?  Overkill?  

[TOtrees]

Seems like a lot of work for... duckweed. 😐 Are you able to get a shallow bowl or container or bucket, and grow your own? With direct sunlight a few hours per day and a couple drops of liquid fertilizer, you ought to be able to produce tons. 

[Tanked]

Last summer I harvested a spoonful or two of duckweed from the local lake. It took a couple of weeks before I had enough to introduce it to the fish. It never occurred to me to go through steps to sterilize it.  I think Vinegar will kill it.  I've been growing it in the outdoor pond, in a bucket, and on the windowsill. There have been no ill effects to the fish.