Can you please tell me what brand of adjustable heater that you use and trust for a betta tank. My tank is 2.5 gal and has a Tetra heater for 2 - 10 gallon, but it is not keeping the water temp 78...it is suppose to.

Thanks
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Amanda Lee~ "I am from The Deep South. Where the Mocking bird sings and the azaleas are blooming!"
Mama to P & V L 6-7-2005
Betta~ Bert in a 2.5 gal tank...living life up good!
2 Orange Sunshine Guppies in a 10 gal tank

I'm fond of the Hydor Theo.  It's compact in size, has an adjustable thermostat, can be fully submerged, and is very reliable.  I always keep two..one currently in the tank, and the other as a backup.  I have yet to need the backup.  

You can find one here.

There are other brands that are good, too, but I haven't tried very many others so can't give you any advice concerning them.  Whatever you do, don't get a Visitherm Deluxe.  I had two go haywire on me and they almost cooked the fish.

Thanks!
_________________
Amanda Lee~ "I am from The Deep South. Where the Mocking bird sings and the azaleas are blooming!"
Mama to P & V L 6-7-2005
Betta~ Bert in a 2.5 gal tank...living life up good!
2 Orange Sunshine Guppies in a 10 gal tank