Buyer beware, unit cannot be calibrated. As accuracy of +or- 2° And my unit is off by 3° your fish will be warm or cold by 8° The bimetallic strips in most heaters is more accurate than this digital unit. I will be using a unit that is accurate within a half a degree it's calibrated down to the 10th of a degree made buy an overseas company I can control both heating and cooling for lesser price. Good job Finnex.

I'm giving this mainly one star because the The heater failed within the first month of use . It Shorted out and I received a jolt of electricity . The manufacturer was pretty much nonexistent and refused to replace the product . The warranty is poor and the customer service is as well . The manufacturer tried to do everything that they could to get out of replacing it. In fact they are now unresponsive. Thankfully I ordered through Amazon was able to get it replaced with no hassle thru Amazon . The second heater has been hooked up for one week and so far so good . I will not purchase another heater from this manufacturer again.

I have been utilizing this 500W heater in my 90 gallon freshwater tank since August 2014. This unit has been great, I unfortunately had a small issue, that was not an issue of the unit. The suction cup on the thermometer release and went out of the tank. the water reached 93 degrees, I had the upper alarm set at 85 and it was ringing loud and clear as soon as I put the thermometer back in the tank. I have since remedied this by placing a clip to the tank so that it won't come out again. The unit has been well worth the money spent!

I am using this in an off-label application: It is heating a 110 gallon deck pond on my back porch (full outdoor exposure). There is a very large pleco in there so I have to be able to maintain a near tropical temperature through winter. Worked just fine outside during this past winter '14/'15 here in New Jersey. I did have this 800 watt plus the 500 watt in there and the tub is fully insulated and covered (in winter). The control box is not for outdoors so I did build it a plastic shelter to keep snow and rain off.
I did water changes throughout the winter which would drop the water temp down. The heaters would kick on and get the temperature back up very quickly. If there was a greater than 10 degree drop, the heater does cycle on and off until it reaches the set temp.
The heater works nicely. The controls are easy to read and to set. The alarm feature works fine. I especially like the digital temperature display. Very easy to read on my way out the door everyday. I do keep a 2nd thermometer in the water just to check up and make sure it is accurate.
The only shortfall are the cords which like other reviewers stated are very short! The unit has to be situated right next to the pond. I imagine with a very deep tank the cord might not reach the bottom. This extremely limits where you can hide the controller and where you can hide the heat tube in the tank.
Outside of the cord lengths, its a great heater though and kept my pleco happy all winter outside!

This is almost perfect keeps your tank pretty much at the temperature you want. The read out is very clear. There are times when it might go up a degree so I just bump it back down. I have two of these. One in my tank and a spare one. When it comes to my fish tank I like to keep spars of every thing just in case I would need and not have to worry about having to get one in a hurry.