Hydor 50W Submersible Glass Aquarium Heater Theo

Heating works good. Been a few months now. And it really excels in areas where normally thermostats could explode. Handled it roughy and abruptly took it out of the water more than a few times. Showed no signs of crack or any other setbacks. Recommended. Quality feels good too.

Excellent product

The thermostat cutoff stopped working after a while and it overheats the water. A lot of people on online forums have reported similar issues. This is dangerous and it can kill the fish!

costly but performance is good, used for a couple of months now

I purchased this in 2013 for a 2.5 gallon betta tank. It worked well for almost two years before I took that tank apart. I set this heater aside for a while until a few months ago, when I was setting up a 2.5 gallon hospital tank for an elderly betta. I set this heater in the tank for three days before adding the fish, and everything was fine. Temp stayed steady. I added the betta.Next day the temp was a few degrees higher, so I turned the dial lower. Next day same thing - temp a few degrees higher than I wanted, so I turned the dial lower. Summer was just starting to I figured it was just higher temps in the house causing me to need to adjust the heater.Next day I went to feed and medicate that tank and the temp was was 94F (34C). Way, way too high. Betta was not doing well. I slowly lowered the temp in the tank with water changes and switched this heater out for a Hagan Elite Submersible 25 watt heater I bought off craigslist in 2014. I have no idea how old that heater is (previous owner had also bought off craigslist), but I've used it off and on for years and never had a problem with temp fluctuations. I've got several Fluval heaters from 2010 that are still in use and reliable as the day I bought them. So even though this heater worked for a few years I expect better for a heater at this price. You can purchase an EHEIM Jager 25 watt heater on here for only $5 more than this one (as of the date of this review) and those are some of the best, most reliable heaters in the hobby.For the record I've tested this heater in an empty 2.5 gallon tank. At the LOWEST temperature setting the temp in my tank was steady at 94F (34C) for more than a week. At the HIGHEST temperature setting the temp in the tank was 84F (28C) for several days before I tossed this heater. So something clearly went very wrong with the temp controls for this heater.

I am happy with the performance of this heater. The construction is good but I do notice that if it is in a tank with low water flow it can get fairly hot if you are touching the heater. So if a fish was to rest on the heater it may or may not get burned? But I think that is a possibility with any heater that does not have a guard. The other thing I noticed with this heater is that the accuracy of the settings varies from heater to heater. I own two of this particular heater and one was off by about five degrees and the other was off by about three degrees. I do have these heaters in low flow tanks which might make the difference on accuracy? It really is not an issue, once I found the correct setting for the temperature I desired the heater performs well. It is completely submersible and seems durable. I am happy with this purchase. I just would make sure you have a thermometer in your tank and to watch to make sure the desired temperature is reached.

I've ordered two of these for my betta tanks. It's been working fine for the last 8 months. One of my heaters seemed to be running a little hotter than the other (85 deg), so I unplugged the heater for 10+ hours and plugged it back in assuming it might help reset the heater. Now it run 5 degrees higher (90 deg). I keep turning it down, and it's not working. My other hydor seems fine for now.Edit: My 2nd 25W heater could barely heat a 2.5 gallon tank. Even when cranked up to max it could barely hit 74 degrees. Clearly a design fault with hydor heaters.

Editing to say I contacted customer service and still haven't heard back from them. I turned this down to 71 and the tank still sits at 81/82.I put the 50w heater in my 10 gallon tank. Set it to 79 and let it go for an hour. When I checked it was 86. I turned it down to 75 and went to bed. Checked it at 330am and it was still 86.7, light still on. Up at 730. It is still at almost 87 degrees. It's going to kill my fish. Going to have to return it and put my crappy preset one back in.

The unit worked for 7 months, then the temperature control died and would not turn off when the preset temperature is reached. The water temperature went up to 100F when we realized the issue and we almost lost our fishes.Went on the Hydor USA site and contact them for a warranty request. (In the meantime, I have to monitor the temperature closely, plug and unplug the unit to keep the water temperature more or less ok. That is troblesome but doable). The warranty coverage is 2 years. First interaction was pleasant when they request photo of unit sticker for batch number, proof of purchase and contact info. With the second interaction, things go quickly downhill: they request that I send them a picture with the electrical chord cut flush to the unit before they will send out a replacement unit.Honestly, I understand that they do not want people to abuse their warranty coverage. They want to ensure the unit is no longer functional and has to be disposed of. But what am I going to do in the meantime before the replacement arrives? (It could easily take days before I will get the replacement unit while I have no way to keep the water temperature warm) Are they going to pay for the lost of my aquatic plants and tropical fishes when the water gets too cold and they die? Customer Support Staff simply does not think things through! (or horrible warranty protocol). Either way, they do not deserve my business.