Milk is a nasty way of making infusoria. Try shaking or stirring it up each day and see if it helps. It normally takes 3-4 weeks before a culture starts to clear.
I personally prefer to use lettuce leaves in a large plastic tub. I use 1 whole lettuce per 20litres of water. Aerate it and keep covered for a few weeks. Then once the water clears and no longer stinks, I take the airstone out, leave the culture for 10mintues and then scoop out some of the infusoria. Then put the airstone back in, add a couple of lettuce leaves and put the cover back on.
You can use most types of plant matter if you don't have access to lettuce.