mate I just came across this now, most of what im going to say has been said already above.
Your sluice needs water flowing through it, think about tossing a rock onto a sheet of tin sitting in the water... its not going to flow off the end.
Drop is also critical to maintain momentum, you want the lighter material to be carried away while holding onto the heavies that requires some decent drop, 9.5 degrees is good fall and you can go steeper if your water is a bit scarce but try to stay around 9-10 degrees.
When looking at the water when setting up a sluice think is there enough flow to move a rock because you plan on dumping rocks into the slcuie all day, if there isn't don't bother or if you have limited fall try to classify a bit and remove the larger rocks.
the end of the sluice need to be out of the water of at least allowing water to fall freely, by submersing it you are essentially putting the handbrake on any forward momentum by meeting it with equal backward force so it will just load up no matter how thick and fast the water is.
you may have seen my videos in Eldorado or Creswick where i set my sluice up buried in the water that is absolutely fine....."If your water has good forward force, unlike the soft curve in the outside bend of a massive river where water slowly falls through your sluice if you want it deep in the water it has to be fast water to clean effectively.
looking at your video i would say that level of flow would be better suited to a 8 inch sluice or one of our new minicell backpacker profiles whihc work well i low flow for classified material
https://highbanker.com.au/collections/sluices/products/6-inch-mini-cells-dream-mat-sluice
if you find a nice rock and level the base of your slcuie up and try to wing dam a bit to get more flow you may be get away with it. if you get stuck or need a hand your always welcome to give me a call my numbers on my website
