Not sure about looping part, it is an interesting question. Due to the non-deterministic nature of physics I don't know if a perfect loop is possible. You might need to do some post-processing. One way I can think of is by cloning the meshed fountain particles and overlaying them on top of other particles at some frame, them slowly making them appear through opacity change.

Yes, you can kill particles by age or collision test inside PFlow and it will work with Lucid.

Marsel Khadiyev (Software Developer, EPHERE Inc.)