Exactly the same little muffin fans that are in computers. These are a little 40mm version. I just covered the non-moving parts with some black silicone and coated them with some organics to hide them. I am always amazed at how long they last despite getting sprayed with water multiple times a day. They will go for years. If you ever need a new one you just wire it in. I think I got the ones in the tank 10 for $10 years ago. Pretty easy to find for a dollar or two. And they are whisper silent especially if they are running at less then 12V which they usually do because they move a lot of air.