How to Reduce Pressure Fluctuation

Hello everyone,
I am trying to find out thermal conductivity of solid Argon at 70K temperature and 0atm pressure. First, I have relaxed my system and then applied fix npt command and finally fix nve command. To fix pressure I used the following command-
fix NPT all npt temp 70 70 (100*dt) drag 0.2 iso 0 0 (1000*dt) drag 0.2
(here, dt=0.4fs)
Even though I run the system for around 30ps I get huge pressure fluctuation. (~30atm).
Would appreciate any suggestion regarding pressure stabilization around 0 atm for solid Ar.

Condensed matter is not very compressible, thus large pressure fluctuations are to be expected unless the system is very large.

To confirm whether you reach your target pressure, you should not look at the instantaneous pressure, but rather compute a (running) average (over a sufficiently large window) with fix ave/time.