Any continuous feeding apparatus, as uhuru stated, is nothing too complex. But, the implications of doing it and the required maintenance of water quality is not easy. Spot feeding is much easier because it is not unlike feeding fish. Sure, you still have to worry about water quality issues, but not really any more than you would with a moderately stocked fish-only tank.
The fact is that continuous feeding, in a holistic sense, is not simple or easy. I've been working with continuous feeding methods for almost 3 years now. The methods for adding food into the tank are not difficult. But, for all the work I've done with it, I still have little confidence answering any of the following questions:
1. How much food needs to be added? - The simple answer is that you feed a ton of food and, with some hope, you're feeding enough to keep your corals thriving. However, it is very difficult, especially with corals like Dendronephthya, to know whether you're feeding sufficiently. Failure with these corals could mean any number of things, not just starvation. Success with them demonstrates that we're at least meeting the minimum requirements. But then, we simply do not have enough success stories to be able to reliably reproduce this success.
2. How much food is being wasted? - My guess would be a very high percentage is wasted. Some of the food will go to feed microfauna that may in tern feed other corals. However, this won't do much good for corals like Dendronephthya, which feed won't feed on pods.
3. With so much food that we are adding, along with likely a carbon source like vodka to help manage nutrients, what are the implications of the correspondingly high bacterial biomass? - Many people have observed thick bacterial biofilms throughout their tank using continuous feeding along with carbon dosing. There is no doubt that the amount of bacteria in high nutrient systems is much higher than in the typical low-nutrient reef tank. We have little grasp of what this could mean in the long term. It brings in the question of the myriad roles that bacteria play in any system. Is it possible that we're setting ourselves up for catastrophe at some point down the line? I don't think anyone has had such a setup for long enough to know.
4. Should we use a skimmer? - I've found that a skimmer is indispensable for keeping these systems. However, as many others have pointed out, it is quite likely that the skimmer is simply removing the bulk of the food that I am adding making the whole system rather inefficient. Perhaps if I didn't have a skimmer I could feed a lot less and therefore would not need it and rely on water changes alone. A lot of people have dabbled with this idea. The problem is that many of these people (and I have the same problem myself) are impatient and want to add the pretty corals immediately. I think if such a system were to work, it would take a lot of time and discipline simply getting it ready to add non-photo corals. No doubt a good amount of food would probably still need to be added, but perhaps this could be a much more efficient and possibly more stable system.
