Works great for glass lip tanks! wont work on anything that has a plastic lip at the top, and my biggest issue is the 1-2 ft power cord they give you. I would have given this a raving 5 star review if they had given a longer longer power cord. Other than that annoyance, the fan itself works great, my fresh water tank runs high in temp and this immediately cooled it down, the fan isn't too loud and has so far done exactly what I needed it to.I bought this for my axolotl tank thinking it was only a short term solution and I would have to buy one of the big $200 ones in the future. I put this in and overnight the temp in the water dropped 8˚ f. Would totally recommend.Great for the price. Does the job with 2 speeds. The ability to adjust the angle is a nice touch and the lip screw allows it to hang off the edge. I just wish it had a timer. It also probably won’t work for tanks with lids.Si funciona, vivo en un país tropical donde la temperatura alcanza hasta 40° en verano el ventilador ayuda a bajar 1 o dos grados sin embargo cuesta que lo haga pero es suficiente para mantener mi pequeño acuario en 28° pero por ser tan pequeño causa vibración en las paredes del acuario espero cambiar pronto de acuario a mis peces y se quite esa vibración.The clip that should be used to mount the fans to the aquarium did not fit my aquarium top. I had to find some way to run some wire thru the unit and to other cords (ie: my power head & air pump) to keep this unit in place. Otherwise fans fell over the back of the aquarium if bumped, etc.The fans themselves run fine. Decent quality/price.I purchased this to draw new air through a bio active vivarium with live plants, lichen and moss. Works beautifully with glass Versatops, both 20L and 55G. Low noise. The connector did come loose and had to be super glued, but this is the only issue and totally fixable. I’d buy it again for future builds.These fans work very well for my aquarium. They do take a while to cool down the tank and few degrees but it works great for the Illinois climate I live in. If you need a strong fan that works quick and you need a cool or cold tank but I suggest these for like 10 to 20 gallon tanks. It works very well for my 15 gallon.Works well to control the temp.