FWIW: I worked with a simple overflow feeder for plankton feeders; Anthias and Genicanthus angels. Here are some issues that need to be dealt with:
1) The overall nutrient input into the system needs to be controlled, it is easy to over-feed with these continous systems.
2) As mentioned, the dwell time must be limited. Non-living food items will begin to decompose in a matter of hours. The container must be kept completely clean and sterile or heterotrophic bacteria will coat the surfaces, waiting for the food items to move through.
3) With living food items (brine, rots and phyto) everyone realizes that the culture water used to raise them must be kept out of the main tank, but sometimes people lose sight of the fact that isolating the living plankton from the culture water, even for a short time, can reduce the nutritional value of the food (except phyto of course).
4) As always, beware of over-extrapolation. Food is NOT available to reef animals 100% of the time. Storms, mass spawning events, tidal changes all can affect the amount on plankton in the water column. Also, predatory animals do not have access to food 24/7, so don't carry this idea over to them.
JHemdal