I have a 55 gallon tank thats been up and running for 4 years now. I also have a 20 gallon tank that I have a few minnows and a larger brim about 3 inches long that I caught out of the retention pond in my back yard. They have been in the tank for about 4 months and are doing very well. I now want to use my 20 gallon tank to start a salt water tank. I just want to put the fish back in the pond but my family says that it would be cruel now that I have domesticated them (lol) Would it be safe to put them in my big tank or could they be carrying some disease that I don't know about even though they look healthy.