He has two pumps in the tank, a canister filter for filtration, and a sump for water level. It looks like in the sump there's a pump that will push water into the tank. But there also looks to be a sort of check valve inline that controls water movement, to or from the tank. You could look into an automated check/ball valve, or do a more basic design with an overflow and a timer.
If you size the sump to hold all the extra water you could build an overflow that's set to your desired low waterline. Then either have the sump pump connected to a water level switch and/or a timer depending on what you want. Then it would just be a matter of sizing the overflow/pump to make the water level change in a controlled manner so that it's not a crazy fast change. Also you'd have to make sure your canister intake is always below the water line.
Basically, timer connected to pump/water level switch, 1) pump turns on with timer, starts filling display, 2) water reaches your high water level mark, 3) that triggers the WLS, pump turns off, 4) then whenever the water level falls below the high mark it will turn back on, repeat 2-4 until timer shuts off. Then just set the timer to do this at whatever intervals you want.
This would require the pump to be faster than the overflow, but neither fast enough to make a crazy fast change. So tank size, water volume, and water volume change would be the main factors in sizing.
Just an idea, I don't know japanese so this is what I literally just came up with. It would definitely require some playing around with, maybe some more equipment. Would definitely be cool though.
