not sure if this has been edited, but if you imagine that last bend in the pipe is coming towards the screen it can make sense. the simplest fix is to move it, but with a little imagination it works :3
1. The reflection of the glass isn't very well done and clashes with the jellyfish on the left hand side.
2. Like tardis said, big perspective problem with the green tank on the floor.
3. the fish looks like it's on the other side of the window pane, right where the character is. Try to make sure that everything looks like its behind the window because now it's a bit disturbing.
4. There's something off about the tentacles of that thing on the right. Just compare the top half with the bottom half and you'll see what I mean (that's nitpicking though although this is what got my attention at first).
5. The floor looks nice but the lighting is off. I'd be great it you could reflect the light from the aquarium on the floor like so: