Particle Sep, Grid Scale and Reseeding? How to set?

[yjcnbnbnb200]

I am making a river scene in Houdini now, one guy said to me that if I reduce particle separation, I need to increase grid scale, and also change the reseed number? And also oversamling in flip solver, I do now know why.

 

The problem i met is that even no collision in my sim and just 200W particles, it cost me 3 min per frame, too slow, my pc has 28GB ram and 24 threads in 3.4Ghz. How to make it fast.

 

Another is if I reduce the particle separation, the over simulation result is different, all the particle seems to be compressd together, I like the shape of high particle separation, want to keep that shape when I reduse the particle separation.