I wouldn't advise you to "keep a cube of bloodworms hanging by it's head"...reason being that any food that is left sitting in tank water for too long will begin to cause an ammonia spike. Also, with frozen bloodworm it's always best to defrost the cube in a small amount of tank water (e.g. in a little plastic pot) then just feed a few pinches of the worms (with tweezers or a turkey baster) and keep the rest in the fridge for the next feed.
If you feed too many bloodworms, the fish can become constipated, too. So a good idea is to feed some squashed pea at the next feed after bloodworms to aid their digestion. Bloodworms shouldn't really be fed every day, either. Try to vary the diet so that they get flake/crisps (no, not the Walkers variety LOL), brine shrimp, daphnia, bloodworms (either frozen, live or those great sachets of jellied foods - TetraFreshDelica range).
Regards, Athena