The 1280 Aquanaut has been around for a long time, I bought mine in ‘86. It was the only detector I used for a lot of years, used it in the fresh water lake and on dirt. After using it for awhile, I found a discrimination setting of 3 worked best for me. Then a few years later I reduced the disc to 2 1/2 to make it even more sensitive. If I went below 2 1/2 then I would dig more iron than I cared to.
Found a good amount of silver with the 1280, I learned to listen for deep repeatable whispers. Max depth in my dirt was 5 or 6 inches on a dime. After a good rain it would go a little deeper.
It gets lighter if you belt mount or chest harness it. If you submerge it in the water, make sure the battery gasket is lubed with something, I used to use a light coat of Vaseline, or silicone grease. Very few problems with my 1280X over the years, they are built like a tank and if you lube the battery gasket before submerging it, and tighten the screws (don’t over tighten), It should do a good job.
I still use my 1280X in the water and an AT Pro in the water. For land hunting I now use other detectors. Good luck with yours.