Aquaponics - Duckweed auto feeder

I've had an idea.

Duckweed grows at an amazing rate. It also seems to spread out to take up the entire surface available to it. This appears to be a function of surface tension. But I may well be wrong so don't quote me on that. In fact, don't quote me on anything.

Because of the way duckweed spreads out over it's available surface, it should be possible to use that, and various other handy attributes of the universe, to make an Aquaponics duckweed auto feeder.

Here's what the original plan looked like.

The pump for my new aquaponics system will be on a timer, and will run for around 10-15 minutes each hour. When it runs, a small amount could be diverted to the duckweed auto feeder. The diverted stream could be applied to a PVC pipe  in such a way as to divide the floating duckweed. If required, the stream could be shaped so it spreads across the width of the PVC, and perhaps points away from the standpipe. If the stream is set to spray across the top of the water, it will keep the majority of the duckweed away from the standpipe, but still allow the water to pass under the stream,through the standpipe and into the fish tank.

Here's the animation that might make it understandable.

Aquaponics - top down view of duckweed auto feeder 

• When the water flows in from the sump pump, a small amount of duckweed is separated from the majority, so that it moves toward the standpipe (to the left) and the rest is kept away to the right.
• The water overflows into the standpipe, into the fish tank.
• The overflowing water takes a "dose" of duckweed with it to feed the fish.
• The size of the dose can be determined by the placement of the water inflow. Moving the inflow further to the right would increase the duckweed dose, to left would decrease it.
• Because the duckweed spreads out to occupy the available space, the dose would be a percentage of what remained rather than a set amount. This means you should never run out of duckweed. If there isn't very much in the system, only a small amount would be delivered.
• The duckweed will grow faster in summer when the silver perch want more feed, and it will grow slower in winter when the fish are not so hungry. The faster it grows the more the system will deliver on each pump cycle.
• If required, a thinner PVC pipe would allow for better fine tuning to allow a smaller amount of duckweed to be delivered each time.

Once it's set up, it should largely regulate itself.

My plan is to make a large bed of water to grow duck weed in, using goat dung for nutrient, and create a duckweed auto feeder connected to my fish tank, that I can scoop some duckweed into every few weeks.

Here's a side view animation