Getting the ACE 400 to work on the wet beach sand is probably a combination of turning down the sensitivity to a place where the detector runs smoothly. Keep your coil parallel to the ground during swings, making sure not to angle it at the end of each swing. Hunt parallel to the water, as different areas will be +/- saturated with minerals including salt.
The sensitivity setting is not a depth control. It allows the detector to still read a target in a heavily mineralized area. If you are looking for silver targets, notch out some of the most obvious notches representing iron. Hunt with the iron audio off. You could probably eliminate all targets from 60's down to the lower numbers, without losing any silver or copper coins. I hunting for gold, remember that gold can nearly read anywhere on the screen, depending on it's size and what the gold is mixed with.
Most successful hunters tend to dig nearly all targets in the water, as aside from coins and rings, jewelry can also show up anywhere.
Below is a hunt I did with my ACE in the water.
https://www.youtube.com/watch?v=8npfSWLvnlI