rober, chalkbrood is a fungal disease and as perry and robo said, there is no treatment, and any treatment for it will just not work.
look in the stickies in pests and diseases for a brief description, honey bee diseases and pests and also a field guide to honey bees and their maladies.
it typically occurs in spring, late spring, cooler temps. chalkbrood can weaken and slow a hive's growth down.
may occur because of excessive moisture in the hive/poor ventilation. i said MAY. i have experienced chalkbrood with adequate ventilation.
colony nutrition, make sure they have adequate pollen and sufficient food stores.
old brood comb? might have to cull it.
other disease? colony stress?
genetics and resistance. as perry mentioned if it doesn't clear up, requeen.