If your shrimp has white stuff growing on it’s rostrum it might be parasites or fungal. It is important that you are sure about the diagnosis because the cure differs.
Have a look at a photo of vorticella parasite on a shrimp here. The symptoms of shrimps suffering on this parasite will be better after molting, because the vorticella grips on the exterior skin. The website recommends using Exit or Punktol (both angainst Ichtoy) in normal dosage as described in the package insert. A friend of mine sucessfully used Sera Costapur: 1 drop per 1 litre of water, the vorticella where gone within two days while shrimps were unaffected.
Photos of shrimp having fungus can be found here. The fungus are most often Achlya and Saprolegnia. The symptons get better when shrimp have molt too but this does not mean that they are 100% okay. As treatment, the drug CILEX (producer: Brustmann) Fungol (from JBL) should help. Dose as recommended. It’s important the that mediacment has Malachite green oxalate as active agent.
This site lists all the active agents of the mentioned medicaments. Perhaps you can find a similar drug if you have problems getting a certain medicament in your country: http://www.rhusmann.de/aqua/medikame.htm
I have not tested the cures myself, so take care and ensure a good water quality overall.

Vorticella (source: wikipedia)