If you're going to feed them, I'd suggest that you feed very little, and infrequently. Take days off--and watch how the fish are behaving. If the fish are somewhat disinterested in eating, stop, at least for a while, and if they stay nonchalant about the food, I'd stop altogether. (My fish still get excited by occasional flakes, but I haven't fed them since Christmas Eve and I'm not sure when I'll feed them next.) Too much food fouls the water, and in winter, there is no plant life to "clean" it up. Of course, if the fish are hungry and eating, there won't be any extra floating around. Just be careful with it. Clean winter water is key, because the most dangerous time for a pond is early spring, when there is a short period of time when dangerous bacteria come to life before the fish's immune system kicks back on. A dirty winter pond heightens the chance of illnesses spreading in that very early spring period. Clean(ish) water at least keeps it to a minimum.
You did nothing wrong by not feeding the fish for a month; most pond owners stopped about that time, except in the warmer climates. Especially given that you have algae, I'm sure the fish were fine, though it can be hard to believe that. On the other hand, if you are very judicious, I don't think you're doing anything wrong by feeding them a little here and there, either. Cold blooded animals are different than other pets, that's for sure. Some pond owners never feed their fish at all. I couldn't fathom that myself, but we all do it our own way.