How can I get a different judge for my custody hearing?

In most jurisdictions, just alleging that a judge may have some prior acquaintance and contact with a party is not sufficient to sustain a motion for recusal. As a practical matter you have to be able to show some direct impact or prejudice created by the contact. If the relationship is close enough, most judges will voluntarily recuse themselves in these types of situations. Talk with your lawyer about this and follow his advice.