Ok, youre answer, helped me a lot. I found a solution.
Now, when I create "blockFxSpark", it plays an animation with only one frame. This frame is void.
When its created, its boolean "isActive" become "true"
When this boolean is true, "blockFxSpark" plays its animation.
And when the animation is finished, I kill "blockFxSpark" and the boolean switch to false.
So now I only have one occurrence of this animation because I kill it. And its probably best like that. ^^
Thanks for youre help.
Here it's a screenshot for helping others. ^^