Your attempt to shoot a watch in the fish tank is not too good.
1) Lighting - The watch supposed to be the main subject in the shot but lighting is badly lighted. More highlight should be added on the body of the watch to give it a more metallic look. The watch is so blue in tone as I understand you are trying to show that it is shot in a water tank and the blue are reflected from the water. But if this is the case, the watch did not stand out.
2) I don't see any water bubbles on the side of the watch. Hence it would be better to shoot the watch separately and not inside the water tank. This way, no bluish tone will be reflected on the watch. Shoot the water tank and props as another shot and using digital imaging to put the two shots into one.
I think using of sprite or 7 up to replace water is not too good. One of the reason is bubbles from Sprite and 7 up are plentiful when you first pour them into the tank. The bubbles will be gone by the time you wanna shoot. I think maybe we could still use water to shoot. After that, using Sprite or 7 Up for another shot just to capture the bubbles and maybe to DI them into one shot later?