[SOLVED] How do I create one object per instance of another ?

Hello community !

I have platforms that can move into water and I would like to create 1 particle for each platform which is going into the water. So, I made this :

But the result is THIS : particles are emitted infinitely because of the loop and I want them emitted only once per platform.

In my opinion, the loop is not a good idea or maybe I'm using it badly. What could I do ?

Thanks a lot.