I want to start breeding copepods in a 10 gallon tank to be able to have them as a food source for my 120 gallon reef tank. What do I feed these things once I stock the tank with them? I am hoping to not have to repeatedly buy $25 bottles of copepods.
Thanks.
Well, if you want something that you'll be able to maintain yourself, you need to start two cultures -- one of phytoplankton and one of copepods. The algal culture needs to be lit, but can probably be smaller than the copepod bucket. The cope bucket should have some light aeration, but doesn't need light.
The algal culture -- you basically want to get that as green as you can, so it needs light, a stable temperature, and some light aeration. You could purchase a culture starter from a store, or just harvest some yourself from a particularly green tank. The main thing is that you don't want any 'pods in it, or they'll breed and eat all the algae.

Probably the easiest thing to use as containers are 2L soda bottles.
You'll want to keep adding algae to the copes -- enough so that the water is still at least a light green when you go to feed 'em again. From what I've heard, at least 2x daily is best.
You just skim out copes with a fine net and plop 'em in the main tank. Refresh the algal water with water from your main tank, filtered to remove any 'pods.
I haven't cultured 'pods before, but I have cultured Daphnia, and from what I've read it's essentially the same process.