We have had a small pond 125 gallons for 5 years. The fountain tends to draw birds to our yard. In winter we have heaters for the bird baths. We tried to keep gold fish outside all winter, with a heater , however, our results were a total failure. Thanks to your articles I found out that the water depth has to be 24 - 26 inches or something like that for the heaters to really work.
This year, I have no idea what my husband fed these lovely creatures, they are huge. My grandson came over to assist in the transfer to the house and a 20 gallon tank. Need I say, he took the 2 biggest fish home to his tank, so the smaller ones wouldn't be as crowded. Along with a heavy duty filter system, my husband placed an air stone along the one end of the tank. The adjustment has been positive, however the question is; do we need to have a heater in the tank? If so what temperature should we maintain? We have it in the kitchen. Our house is old and drafty, we keep the heat at 65 degrees.
Many thanks for your asssitance and information over the years.
Marge

Nope, you don't need a heater. Keeping them cooler will mean they eat and poop less so the tank stays cooler. 65 degrees F is perfect for them! You can even keep them in a cooler location, down to even 40 degrees F. If kept below 50-55 degrees F, you don't have to feed them at all. At 65 degrees, feed them a little once a day. And next year, you'll need either a larger/deeper pond or a bigger tank to overwinter them!

Many Thanks.
I appreciate your imediate response. The tank has a bit of an odor to it. Should I invest in a tank cover? There is no light.
Marge

What kind of odor? If it stinks, it may be time for a water change! It's up to you whether you want a lid or net on top of the indoor pond but goldfish do jump so it's a risk. I have 17 baby goldfish in a 20 gallon tub in my basement. I opted not to cover it this year, hoping they are smaller and won't jump. So far, so good. In past years, I had white clouds and guppies in there and they did jump so I put mesh window screen over the pond. If you don't have live plants, then intense lighting is not required. For the health of the fish, they should have some light, even if indirect to see their food and have a sense of night and day. If there's a window in the room, that should be enough. Hope it works out!