Adjustable aquarium heater-newbie question

[Lori]

I need someone to tell me the best and safest adjustable aquarium heaters for small tanks. Two 10 gallons and a 20. I have preset aqueon heaters that just aren’t keeping the water Betta warm!  
ive heard horror stories about heaters cooking peoples fish, so I need a brand I can trust. 
thanks. 

[Lori]

I need an adjustable. I have a preset in my Betta tank and I can’t get the temp above 75. 

[Tetra Guy]

i have tried several, including the german made adjustable Eheim which was very inconsistent.   The best most reliable heating has been a pair of inexpensive preset Fluval heaters coupled to an Inkbird thermostat. Thermostat is set for 77. Heaters  preset for 78. Redundancy and excess capacity provides some safety and consistency. 

 

[CT_]

 

40 minutes ago, Tetra Guy said:

The best most reliable heating has been a pair of inexpensive preset Fluval heaters coupled to an Inkbird thermostat. Thermostat is set for 77. Heaters  preset for 78. Redundancy and excess capacity provides some safety and consistency. 

 

This.  A heater+thermostat as one piece is a difficult thing to get right especially for cheap and especially when encased in something not very thermally conductive like glass.  It becomes a pretty trivial problem when you can move the temperature sensor away from the heater some.  The cheap non-digital heaters also use a bimetal thermostat which have a lot of hysteresis, but work great for a backup shutoff incase something goes wrong (for example your temperature sensor falls out of the water).