instability of simulation after change fluid density

hi everyone
i'm new to CFDEM and run my own case that use air as fluid and everything is okay after that i changed my fluid to water(without change anything else) and after i run the simulation , the result is unstable and it's look like to need change some parameter
fluid velocity=particle velocity=0.05m/s laminar dem time step=0.00001 cfd time step=0.0001 and if need more information i will share it
if you have some experience please share it with me
thanks
best regards