I'm not extremely familiar with cryptosoridium. From what I understand, it is a parasite found in water. Is this correct?
Have you looked into N'Zymes Ox-E-Drops? It is a 5% solution of sodium chlorite (like a weak Miracle-Mineral-Supplement ). It is supposed to be anti-bacterial, anti-fungal, and anti-viral. I used to put it in Haley's water (just a couple drops), but I have been giving her distilled water lately.
I didn't think of it before, but Haley has a skin infection, and I may try using a dilluted solution of it to rub on her skin. I have actually been using the Humaworm medicated cream on it some, but the infection is stubborn.