went to a friends house and they were given a 10 gallon tank. The previous owner put some water in it and killed all the
goldfish, one pelco about 6 inches survived. They never turned on the filter and he had been sitting in it for about 2 weeks with no filter.

When I got him and the tank, the water was black and slimy. He kept sticking his head out of the water... (was that a sign of distress or trouble breathing?)
I transfered him to my tank at home, it is a 10 gallon too, but plan on moving him to a 55 gallon one soon.
Anyways I scrubbed and scrubbed the one tank I brought home. and have it cycling. How long do I have to wait to add fish?
I don't have a heater for the new one. I was thinking a couple of fancy goldfish and some snails... Is there any other fish that do ok in a cold tank?