Man this is pretty hard, even for normal difficulty.
Reviews for "Bubble Tanks TD 2"
Great game, but the difficulty needs to scale faster in the survival mode. The game restarted when I logged in, but I was around wave 2600. I had four mega-mega towers built and they hadn't let an enemy actually get on screen since about wave 200. I was planning on leaving the game running overnight to see if it ever runs out of waves.