I kept many tanks of plecos from the Xingu which at the peak of the dry season can see water temps in the low 90s. If I have to runb a dry.raint season I get the tanks up to 92F before in 24-36 hours I drop the temps into the 76 range. After that I plug heaters back in and move it to 80-82F. I normally keep the tanks between 82 and 86F.
So I have no choice but to use heaters/ I also consider them to be the least reliable piece of equipment we use in tanks. For the pleco tanks, I have all the heaters attached to a temperature controller. But this only protects against heaters getting stuck full on and making fish soup. A controller cannot help when the issue is heater failure and the subsequent drop in temp.
Almost all of my tanks have two heaters. My favorite and most reliable heaters have proven to be the Hydor in-lines. But I only use them with canisters and I often have a second in tank heater. I do not hook the in-lines to a controller. I had 3 such heater in use until I started to downsize. One finally failed and I had to replace it, but that was over 20 years in use before it happened.
To protect against the controller failing in some cases I set the heater a couple of degrees higher than at where the controller is set. This way if the the controller just passes current but does no controlling, the heaters will still come one to keep the tank warm. I normally feed tanks close to daily, so I can usually detect when a tank is too cold. It the controller fails to turn of the current, the settings on the heaters act as a back-up.
To date, almost all of my heater failures have been on the too hot side and never a failure to heat. The use of dual heaters in tanks has saved me from a single heater quitting and a tank getting too cold. Two heaters also work more effectively than one as the heat is generated in different parts of the tank. I also almost always place them horizontally near the bottom of tanks. Heat rise and this configuration provides maximum heating. Further, since heated water rises, this configuration gives the best boost to circulation as well as heating. it pulls water from the bottom of the tank towards the surface. it also makes it easier to hide heaters so they are out of sight.
