I would suggest changing the instrument at around 00:25. While it feels in place, the quality/sound (?) is kind of weird here.
I love the beginning, it gives off a great water feel, especially with the drums and the airy sound.
I think you lose the underwater feel when you start going prominently drums. Especially at 1:31ish, here, it just feels like it's a mostly percussion piece, rather than the percussion being a background to simulate the water feel.