Tube worms and feather dusters do not need light as they do not contain zooxanthellae. The coco's definately need good chem levels for their calcerous tubes though. If the tank is not stocked with too many types of calcerous animals, regular weekly water changes should suffice but be sure you test the alk
regularly to be sure.
What liquid foods? Many prefabs are just exspensive water that quickly foul the water. Might wish to look into a good homemade <<blender mush