I built a box about 3" high. 6 " and 48" long. As you can see, it tapers to a sharp end. There is a weight at the other end that is made of steel and is in-cased in plastic.
As the water starts filling the tray, it pools in the lowest part (shown in dark blue). As the tray takes more water it fills to the left in this picture. At some point, the water to the left of the fulcrum weights more than what is on the right and the weight of the steel. At the point the bucket tips over and dumps it's water. The water rushes out of the tray to create natural high speed, fairly linear turbulence.
The water spills a foot, in my case, to create a splash. To prevent over-splash, I installed a tube that goes just below the water line. I also have a flat plastic plate that stops the popping bubbles from causing salt creep.
When the water finishes dumping the tray rights its self. I placed jell pads, like you might put under your wrist when you use a mouse or keyboard, under the counter weight and at the sharp end to prevent a bumping sound and this works quite well.
Unlike similar the designs in Dynamic Aquaria, I place the fulcrum on the outside of the bucket. That way, I could move it forward and back until I had it properly tuned.
When the bucket tips back up, it happens quickly and the remaining water that doesn't make its way out of the tray, reverses its path and slides back down the narrow end of the tray. Then it crashes into water at the right end of the tray and into the wall of the counter weight. This adds random erratic turbulence. While this is not advisable, I found that I could leave my scrubber unattended for weeks or even a couple of months without seeing any dye off.
This is a design that requires basic fabrication skills and access to a ban saw or something like it because you need straight clean lines. Cutting the angle does not lend itself to doing score and snap cuts which is what you normally get at Lowes. Other than that, it wasn't too hard to make. I bought 1" square bar stock and they cut it for me so that I had four pieces to stack into a 4" height x 4" length x 6" (minus that plastic) width.
I did have to mess with it for a couple of weeks to get it to work the way that I wanted it to. This is definitely not something that you can just take out of a box, plug it in and forget it. Once I tuned it, I haven't had to mess with it much at all though. It is very forgiving.
