How to keep beer warm?

[Abel]

I am brewing a Berliner Weisse and need to keep my beer above 90 degrees for when I add the Lactobacillus and was wondering if anybody had an tips on doing this?
I was thinking a fish tank warmer, while the carboy is submerged in water? I just don't know any other way to do this so any help would be greatly appreciated!

 

[BreezyBrew]

Ethier a heating blanket or a fermentation wrap. Be careful though they can get too hot.

 

[Calder]

I use a small heating blanket wrapped around the side. I only use 3 gallon fermenters for my BWs. I stick a thermometer between the blanket and the fermenter, and it reads 110 F.

You should be able to get it in the mid to high 80s in a swamp cooler with a fish tank heater.

You don't have to keep it up at 90 F, lower will work. Probably need a minimum of 70 F. At lower temperatures, it will take longer.