I went throught the same thing when I setup my 20. I opted for a different tank, but kept the same filter and heater that I had used copper with. I made sure to give it a few good washes and I changed all the media on the filter. I ran carbon on the tank when I set it up and tested the water for Cu shortly after. There was 0 Cu in the water. I say get a different tank, which for a 15gal should be more then $20-$25 probably less, and keep the filter and the heater.