Leave the blanket weed alone unless it is really thick as the baby fish will feed off tiny things in it if they need to and also hide in it from predators. My pond is well established and I stopped feeding my fish in november. I wont feed them again until see them actively up and looking for food on two or three consecutive mild days and even then I will only put in a tiny amount of food and early in the day. When a fish has swallowed food, if the temperature doesn't stay up to keep the fishes metabolism working while the food is digested and the waste excreted, when the fish goes back to semi hibernation, the food will stay in its gut and could decompose and make the fish ill. The risk of this happening is greater with prepared food than with what they will scavenge out of their environment as this has a greater concentration of nutrients in it