BAD ODOR in new 40 breeder tank with 2 fancy goldfish

[Low Rider]

Can someone please help with some advice. I recently purchased a 40 breeder aquarium and put 2 juvenile fancy goldfish in it. Within 15 minutes I noticed a bad smell. It smelled like vomit / a filthy disgusting lake. Just a very gross smell. Maybe a hint of rotten eggs to it. I used a Giant seeded sponge filter from another cycled tank . The ammonia levels were 0 ppm. nitrites 0ppm and my nitrates were the lowest I've ever seen like maybe 5 to 10 ppm. I have no idea why the tank smelled so bad. I tried everything. I bought lots and lots of carbon. I bough chemi- pure, purigen. I even added an adittional marineland penguin pro hang on back filter. So that was 2 filters running. One was the 375 gph and the other the 275 gph. And still the smell was just as bad. One week went by and I gave up. I brought the fish back to the store that I had purchased them and decided to call it quits. I did a 100% water change and the smell has drastically reduced. It's basically almost completely gone. Did this happen because gold fish are just very dirty fish with such a high bio load? The tank smelled fine before I put them in there. Should I get rid of all of my substrate / plants/ decorations and start all over? or can I just keep that in there and just wait a little while? Will this possibly happen with cleaner tropical fish like tetras? or was it because of goldfish? If anyone has any type of answer please let me know I would greatly appreciate it. Thanks.

[OceanTruth]

I kept Ranchu goldfish for years and never had an unpleasant odor from the tank. I have no idea what it could have been. Maybe something was off with those particular fish?

[Low Rider]

Yeah perhaps the place I got the goldfish from was feeding them a bad diet. I've done so much research and no one else online has complained about goldfish having bad odor. The smell is roughly 70% better but there's still some remanence of it even after doing 100% water change. I never changed any of the filter media that's probably why.  Right now my tank is empty. I'm going to try other fish with a low bio load in the hopes that there will not be any bad odor. Thanks for getting back to me.

[Struggle]

Id change one thing at a time, it might be your water causing the smell. When our lakes turnover due to the seasons the tap water has a rather bad smell.