43% of 177 verified Cobalt Neo-Therm Heaterowners don't recommend it, and 14 describe specific problems — based on real owner comments from Reddit, enthusiast forums, and YouTube.
For balance: 51% recommend it. This page collects the complaints so you know what you're signing up for — read the full owner report for both sides. How we score
“I hate things that only come with one suction cup”— @trudeaumustgo1920 on YouTube
“Doing some more research into the Neo-Therms, they seem to fail --as in explode -- far too often for my comfort. Reviews complaining of that I read were as recent as this year.”— Barliman on Aquarium Advice
“My first and hopefully only tank crash occurred two years ago with a NeoTherm which stuck in the on position while I was on vacation. Cooked the entire tank.”— NPD_289 on Reef2Reef
“I have run the Cobalt Neo-Therms for years in my DT(s). Very true to keeping temp. Eventually water starting getting into the casing and then another got stuck on and nearly fried my tank.”— tkd on Reef2Reef
“I have had 2 overheat the tank. I had two 75 watts in my 36 gallon. I few months ago I noticed the tank temperature was 81 (it’s usually 75) and the heater light was set all the way up on one.”— Dedife on FishLore Aquarium Forum
“I had a Cobalt Neotherm split open end to end just when it was soaking in some fresh water, so I can attest to quality control issues with some of the previous lineup.”— blaxsun on Reef2Reef
“had one of these fail after 6 months, water temp was set at 77, heater glitched to 92. I was traveling at the time and this cooked my coral and my tank. In damage control now.”— MerkWert on Nano-Reef Community
“I thought that this heater was accurate to +-.5 degrees? It seems that it is what is keeping the tank to hot when set at 78. I wanted to get some opinions before i called cobalt for a warranty replacement.”— Cycleguy0623 on Nano-Reef Community
“my Cobalt Neotherm showed the temp in the red section 90+ while the setting was 82*. This is the second of these highly rated heaters that has overheated.”— Fishrev on FishLore Aquarium Forum
“I've owned my neo-therm for only 6 months, I woke up this morning and my clowns looked panicked, my hammer coral dead and my other corals don't look good at all!!! This heater went rogue and turned itself up”— Sirshots on Nano-Reef Community
“I had two different neo therms fail on me. One I caught before it did any damage; the other (which was a replacement Cobalt sent me) wiped out a tank.”— MChambers on The Planted Tank Forum
“I just had a cobalt neotherm heater blow up in my sump!!! I heard a loud noise, and thought it was my dogs...I could see smoke!!! A lot of it!...My gfci didn't even trip though.”— fifthtoe on Reef Central Online Community
Not complaints — practical notes from owners that didn't affect the score.
“I have it in a 10 gallon and it's set to 76 degrees, but the temperature in the tank ends up being 77. If I set it to 78 degrees, the temperature would end up at 79 degrees”— Seadragon on Nano-Reef Community
“I pull the plug on the one in the bucket once a week and it comes right back to the same set temperature.”— NY_Caveman on Reef2Reef
“Mine is set at 80 and keeps the tank steadily at 78. It's close, but not dead on.”— Kellie in CA on Nano-Reef Community
“I'm having an issue where my Neo thinks it is 81 when my Apex thinks it's 78.”— SerenityReef on Nano-Reef Community
“I can say my tank temperature has varied from 80.31-78.10during that time.”— Gareth elliott on Reef2Reef