Missed this post:
Wow that did a GREAT job with the duckweed. I guess you took those larger pieces of leaves out with your hands first?
Any chance a fish could get sucked in and stuck in the DD until you come to rescue it?
Yes, I first de-bulked the pond scum in the tank by removing all the Bolbitis then using a large net to scoop out the bulk of stuff. But then, replacing the Bolbitis, all those little bits of duckweed that got stuck to the Bolbitis as I lifted it out then came off the Bolbitis and over days have floated up to the surface. The DKDD removed all that made it to the surface, now each day I find a handful more that have made it up to the surface, and I remove them by hand. I sort of beat the Bolbitis to loosen them, the way one beats dust out of a dirty throw rug, if you will.
The waterfall only sucks about 1/4 inch of water depth off the surface, so you'd have to have a really surface dwelling fish to even be in the zone.