When taking damage the zeros go in the box on that ships mat. Do the zeros return to the chit pool after the round ends? At first I thought this made sense to do but couldn't find it in the rules.

Having thought on it I'm now thinking they stay on the mat as this helps to maintain the balance of chits in that pool and not dilute it with zeros.

What happens if the pool runs out of chits? (It may not be possible with four ships)

Thanks in advance!