Z.Z. Portal needs.. changed.
For starters, I like the idea of Z.Z. Portal; I think it adds a nice new strategy to the game as far freezing lanes and supplying push potential.
That being said, I believe the portal itself should have a 5-hit kill, the same as Pink Wards. As well, the minions are quite finicky when it comes to damaging them and it can require multiple hits to destroy them.. I understand that you don't want the portal and its minions to seem super vulnerable to the elements and render them useless. I just believe, after having gone against enough of them, that they have a little too much power at the moment.
I'm not sure how to change the minions, but I'm sure you can figure something a little more legitimate with them.