I stored my phage in 20% Glycerol at -20'c. After 2 months it still had function but after 4 months it lost its function and was not able to produce a plaque on a plate. Also, its titer for SDS-PAGE was so low. What are your ideas?
have you tried to save them using glycerol for storage in -80C? my suggestion: add 15% glycerol to your stock and mixed it gently (maybe need vortex), then freeze it in N2-liquid completely and put it in -80C.