Ideas to Pinpoint Performance Issues (Unity Indy)

I’ve just finished my first game and published it to the Play store but I’ve since noticed a performance dip that gradually gets worse the longer you play (not sure why I didn’t notice it before). The game is a simple little Zombie shooting gallery style game where you blast zombies with fireballs. I notice a dip in performance after killing 100 or so zombies. I’m looking for ideas on how to find the source of the problem.

Here’s a list of what I’ve tried so far:

    1. got rid of instantiate/destroy and
      switched to object recycling/pooling
      and enable/disable for zombies,
      fireballs, most FX
    1. disabled audio
    1. disabled spawn FX
    1. disabled death FX
    1. commented my debug statements

none of the above had any noticeable effect on performance

Before changing from instantiate/destroy to object recycling I disabled the script that makes the zombies move toward the player and allowed MANY to spawn, there was no noticeable performance hit until I destroyed several of them. Play store still has the version w/o object recycling for the zombies.

I don’t notice the performance hit when playing in the editor. Stats are as follows: 150+ fps on while playing in editor, Main Thread 902ms Renderer: 5.3ms, Draw Calls: 34, Tris: 782, Verts: 1.3k, Used Textures: 22-37.6MB, Render Textures: 6-6.8MB, VRAM Usage: 9.9 to 41MB, no shadows, animations.

As you may guess I’m pretty new to the whole programming/game dev thing but I’m doing my best to learn from my mistakes. Any input even and especially criticism is appreciated. If you have ideas on what else I could check to find the issue that would be great. I realise it’s a long shot w/o the code but I wouldn’t know what code to post at this point. If you like, here is a download link to the game:
https://play.google.com/store/apps/details?id=com.FunForgeGames.ZombieBlastInfinity

I had been using the detonator explosion framework in this project and it was the culprit. Detonator works fine on all but mobile and even with mobile you won’t see problems until your game has been running for a bit.