I've built a few of these in the past as an alternative to store bought ultrasonic humidifiers. Even the smallest capacity models are around $35 - $50, but you can build your own, for way less, and with larger capacity reservoirs than most of them. For those who aren't familiar with ultrasonic humidifiers, aka "ultrasonic foggers", "nebulizers", "atomizers" or "cool-mist humidifiers", they are a great way to add humidity to a grow, without adding heat. I'm not going to go into how they work. There's plenty of info out there. I just want to show an alternative method. There are other tutorials out there, but I don't recall seeing one set up like this. So here we go... This is what it looks like Parts:. Nebulizer w/power supply (Amazon, $12), tall, thick plastic cup, pet water bowl with reservoir (this one's 2.5-gallons, but they go up to 5-gallons), and a small aquarium pump. The pet water bowl is the perfect depth for the nebulizer to create fog, and will last a really long time. The nebulizer creates a lot of water droplets that will get everything wet, so the tall cup contains any spray. The aquarium pump is to jet the fog out of the cup. The very smallest will do. You can also use a fan and draw the fog out. Either would probably do fine. Pic of the nebulizer. Using these instead of store bought humidifiers allows you to replace the discs for real cheap, or even the entire nebulizer for as little as $6.99! It's way less expensive than having to buy a new ultrasonic humidifier! Drill a 1/4" hole a couple inches below the rim, then cut the cup from the rim to the hole. This is to hold the power cord, and the nebulizer in place. You want to use a thick cup so it's less prone to cracking, and it helps weigh it down in the water. Drill three more holes around the cup, but this time, only an inch from the rim. These holes allow the water to get to the nebulizer. Next, drill small holes towards the base of the cup. These are where the fog will jet from. You can drill them around the entire cup, or on one side, like mine, to jet the fog in a single direction. Experiment, and see what works best for you. These holes should be much smaller than the previous holes though, otherwise droplets will spray out and you'll end up with a wet mess. I used a 9/64" bit for these. Also drill a 1/4" hole in the center for the air line. Thread the nebulizer cord through the hole. You don't need to give the nebulizer cord any slack on the inside. As long as the nebulizer is upright. Now just put the air line into the hole, and plug everything in. Use the air limiter to adjust the amount of fog. If your pump didn't come with one, your local hydro store should have them for a quarter or so.