Review on 🐠 Efficient Heat Control: Hydor Submersible Glass Aquarium Heater - The Original Theo by David Golden

I bought this for a 2.5 gallon battle tank. The 25 watt cobalt neothermal heater I used in an old nano reef tank didn't work as well in low flow tanks so I settled on the 25 watt Hydor. I have a temperature sensor and aquarium controller in the aquarium to monitor temperature and control lighting and at first the Hydor seemed to work fine and heat the aquarium slightly. Unfortunately the temp continued to rise even though it was set at 77. If my aquarium controller hadn't cut it off at 80 degrees, it would have kept going up. Setting it to 75 gave the same result. I saw another post where someone had to set it to 72-73 to get water at 80-82 degrees, which is too much of a difference for this thing to be reliable. There's no doubt that this thing can heat water, but I would highly recommend getting an Inkbird controller and temperature sensor like this one https://www.amazon.com/gp/product/B07QWTJNX2/ref=ppx_yo_dt_b_search_asin_title?ie =UTF8&psc= 1. if you don't want to cook the fish. Update: I bought a 50w version for another tank to see if I had better luck, but the unit I got didn't even start turning on or getting hot without me set it to 87. Thermostats for these things are all over the place.