Well, it's doable I suppose... except perhaps the pH monitor (I haven't seen a digital one anywhere... I've always used litmus paper (good old bio class :)) It seems like quite a lot, but I would get an arduino mega, just in case (you'll be using a lot of pins)... Also, start basic - try each of the seperate "systems" you've described seperately first, then start adding them together to finish off your product.
P.S.: For waves, don't use motors, use servos, and swing them back and forth with paddles, simpler circuit and better results...