Review on 🐠 Hygger Titanium Tube Submersible Saltwater Tank Aquarium Heater with Digital Thermostat, IC Temp Controller - 50 to 200 Watt by Clare Thoms

"We do not recommend the use of this thermostat with other brands of heaters due to safety reasons." Another heater with a built in thermostat SHOULD be used with this controller. If the temp sensor is pulled out of the water (this happened to me and I didn't notice too late) or if this controller fails (other reviewers had this issue but not mine), the heater stays on. and kill your fish. The controller uses a simple mechanical relay to turn the heater on and off, so you can use ANY heater (or combination of heaters) that doesn't exceed the controller's power rating (500W for the HG-902). controller, 200W for HG-802 controller). Use a heater with a built in thermostat and set it slightly higher than you would like (but not so high that it harms the fish). If that controller then fails and the heater doesn't turn off, your fish are protected. Also, the product description states that this heater cannot be used in an acrylic aquarium (probably because the "Titanium" heating element is not shielded and gets very hot). However, this allows you to use a shielded heater or, for more even heat distribution, TWO low wattage heaters (no more than the maximum capacity of the controller in total) connected to an AC splitter. This is how I use mine and it works great. You may be wondering if you are going to be using a heater with a built in thermostat anyway, why use this controller? Well, this controller is MUCH easier to adjust than those little knobs on most aquarium heaters, gives you a large, easy to read display of your aquarium's temperature, and offers the backup protection discussed above. I really like this product and wish the controller could be purchased without a heater as it is not safe to use with the included "Titanium Tube" heater. By the way, if you're electrically savvy, you can even use the HG-802 controller that comes with the inexpensive 50W, 100W and 200W models to switch a powerful external relay. You can then use ALL the heaters you want, up to the maximum rating of your external relay. Kilowatts and Kilowatts! I'm planning to do this with a 1600 gallon indoor pond I'm building right now. Heck, you can even daisy-chain two of these controllers (both sensors in the water, the first controller set to a slightly higher temperature) for added security. One controller can fail, but it is extremely unlikely that both will fail at the same time. Your fish will thank you for staying alive.