I dont know goldies well. I know they are dirty but you could try. I would get several uv sterilizers with VERY slow flow to kill everything in the water. Loads of plants. I mean ALOT! Pick plants that really absorb stuff too! Get some pothos vine and hang the roots in the tank. Setup a nice sump. I dont know that it would work. I wanted to do something similar but not with dirty fish so I dont know.