Towards the beginning of the movie when Zack is doing fish impressions on the fish tank glass, Cody, the doctor and Mr Moseby change positions and hand/arm positions between shots.
When sea wall breaks nothing should have been sucked out as water pressures would be equal on both sides.
When Dr. Olsen and Dr. Spaulding are facing each other Dr. Olsen is shorter than Dr. Spaulding but when Dr. Olsen takes off the mask and shows that he is Dr. Spaulding's twin, Dr Olsen and Dr. Spaulding are the same height.