Aquatabs are not effective against Cryptosporidium Oocysts.

Those are quite tough bastards. Here the options for killing crypto:
Ammonia (5%, 30 min, 22 °C, 97% reduction),
hydrogen peroxide (7.5%, 20 min, 20 °C, >3 log reduction),
heat (72.4 °C, 1 min; 64.2 °C, 5 min),
ozone (12 mg/L*min, 20 °C, 3 log reduction),
UV (254 nm, 22 mJ/cm^2, 4 log reduction),
Solar irridation (830 W m^2, 40 °C, 10 h (30 kJ)),
Gamma irridation (400 Gy),
Chlorine dioxide for 3 log reduction (water temperature, mg/L*min Chlorine dioxide): 1 °C, 1830; 10 °C, 830; 20 °C, 347).

Of these, I'd say UV, heat and Chlorine dioxide are the most sane options for you.