Green spotted Pufferfish and goldfish

Question
Hello.  My name is Allison and I am inquiring some informaiton about Pufferfish.  I have had Greenspotted Pufferfish for about 2 years and I have noticed that the tanks get really dirty really quick.  Is it safe for me to stick a goldfish in a tank with four Pufferfish?  Or will the pufferfish eat the goldfish?
I just got a new 20 gallon tank.  I have 4 pufferfish and one male fancy skirted guppy in there.  If you can respond that would be great.  Thanks!

Answer
Hi Allison. You really shouldn't even have a guppy alive in a tank that houses puffers but for some reason they seem to be leaving him alone for now. While a large goldfish and a puffer would be fine together as far as fighting goes it would no be wise to add a fish that is extremely dirty, like a goldfish, to a tank that is already having problems with being dirty. Goldfish are also cold water fish and can suffer from all kinds of fungal and bacterial infections if kept in a tropical tank that is kept heated. Goldfish are best left to ponds and unheated tanks.