I wanted a way to humidify my terrarium for the benefit of the orchids that live there. After much tinkering I came up with this system. I call it a cloud maker because it generates an extremely fine mist that hangs in the air. Although this system is fairly small, it will fill a 50 gallon tank in under a minute with an opaque cloud.
The system is fairly simple. Please refer to the diagram below. I constructed the reservoir from a short length of PVC piping with a matching cap siliconed in place at one end. At the bottom of the reservoir, I siliconed an ultra-sonic fogger that I purchased at a local pet store. On the side of the reservoir, above the water line I inserted a plastic tube to act as the outlet for the mist. The lid is from an Ikea cookie jar that just fit perfectly. It is made of aluminum and has a soft rubber seal. On the top of the lid I mounted a small fan from an old Pentium CPU and cut an indirect path through the lid. This allows the air to blow in but prevents water drops from flying out the top. The idea is that the fan pressurizes the air space above the reservoir. The fogger sprays a fine mist into the pressurized air and it flows out the side. In my case it is piped about four feet up from the floor to the top of the aquarium.
Here you can see the effect of the cloud maker after about five seconds of operation. It is very effective. If left on for a full five minutes, you won't be able to see into your tank.
Here you can see the outlet at the top of the tank and get an idea of the rate of flow.
Here you can see the cloudmaker from overhead. The device is connected via a ball valve to the filter's outlet so that it can be filled with water without a trip to the sink.