Hi I have a pond goldfish that I believe has swim bladder, I have transferred him and his friend to a 50L nursery tank with Weed, I put aquarium salt on saturday and yesterday put swim bladder medication in, he doesn't seem any better, I under stand the water temp should be around 80 Deg F. At the moment it is only around 50 Deg f how do i increase the temp while the fish are in the tank?