Can anyone tell me what type of goldfish these are.  They were given to me and were raised in a whiskey barrel that was cut in half and fiberglassed. (app. 30 gallons)  I moved them into a 250 gallon tank that is filtered and aireated.  They have been in this tank for a couple of months and have done very well.  I am worried about the water temperature because I can't find a heater big enough to work on this size of tank.  It is on my front porch and is covered but still out in the open to the atomospheric elements.  I live south of Houston, TX and the temp doesn't normally freeze but the water temp has gotten as low as 46 F.

Goldfish like Fantails and Ryukins can survive pretty low temperatures. They've been known to survive in iced-over ponds, as long as there is a hole in the ice to allow the water to breathe. In colder temperatures, they will sit quietly on the bottom of the tub and not eat a lot. It's a form of hibernation. Don't feed them a lot when it's cold, as the food won't be eaten and will just spoil the water.

My pond reaches temps of about 5 degrees celsius in winter. The fish become slow and sluggish and stop eating. When the weather warms up in spring, they become more active and start to swim around. (The pond reaches about 25 degrees on a hot day in mid summer, just shows how wide a range of temperatures goldfish can withstand.)

I had a tub pond with two small comets. To keep it warm, I placed potted plants around the tub, which sheltered the water surface from cold winds and insulated the tub. I placed a light above the tub, and this seemed to warm the water considerably. The light created a fertile breeding ground for algae, though, so I had to put more plants into the tub. I think the new plants, along with the light, helped to keep it warm in there.