What type of dredge set up are you using ? Suction nozzle, jet log with/without flair, crash box or something other ?
Pics would be helpful.
Something I was thinking about Brad touches on.
At the outlet of your discharge into the box, do you have a baffle to smooth out the water as it enters the box ?
If not, employ one. A piece of rubber (mud flap). Helps smooth out the water, slows the water some, helps to settle the gold in the box.
Also, does your box have a scalper, or punch plate over the upper section of the box ? The material moves up and out of your jet, dropping onto the scalper.
This allows the small stuff drop through into a slow water area, keeping the larger rock moving off the sluice.
As for volicity, you want enough water to clear the box in about 10 -15 seconds, that may mean suction may suffer some, better to slow down and not blow gold than to hog it through loosing precious gold that one has worked hard to obtain.
Try to keep the box discharge above and out of the water.
Its a combination of all the above. Enough slope on the box to clear in a reasonable time, not to steep, enough water flow to maintain a reasonable nozzle suction to keep material moving through the hose and not clogging but not over powering, able to run motor/pump at something less than full throttle.
Are you running an air compressor ?
Its just that simple....
Brad, call me Bill, none of this Mr Hall stuff please.