torn fins, bullied goldfish

Question
Hello,
I have a medium sized (3.5 inch) telescope eye goldfish in a 10g filtered tank with 5 guppies. The tank has been up for 1 month, and nitrites and nitrates are undetectable. PH is 8.0 and that's what it comes out of the tap as here. Temperature is 73 degrees, and I do a 10% water change every day or two, but for some reason yesterday I decided to do a 30% change. I always treat the water to get rid of chlorine and chloramine and add aquarium salt.

This poor fish came home from the LFS 3 weeks ago with an anchor worm attached that I did not notice in the store. I isolated the fish for several days, removed the worm with tweezers, and treated the entire tank with a product called Parasite Clear (one tablet every 48 hours, done 6 times) as well as copper sulfate. All seemed well after that.

Today I came home to find the goldfish nose down and vertical in the corner with tailfin and dorsal fin shredded. It looks to me like he may have been seriously beaten up by his tankmates (I've learned my lesson...never mix goldies and guppies). He's also missing a few scales. No signs of ick, no anchor worms, velvet, or color changes. He isn't gasping. I think one of his gills looks injured (reddish and the edge is folded over a little bit) I've isolated the fish again. He's already in water treated with copper sulfate, parasite clear (which contains the antibiotic metronidazole, as well as praziquantel), and salt (I dissolved one tablespoon in 10 gallons).  He looks like he's gonna die but is there any last ditch effort I can make to save him?

Answer
Hello,
Goldfish should not be kept with tropical fish, because they require different temperatures. Your temperature is a bit too high for goldfish, yet a  bit too low for guppies. In the future, try setting up a cold-water tank AND a tropical one if you are going to keep goldfish and guppies.

Did you actually notice the guppies attack the fish? Guppies are usually very peaceful and hospitable, I'm rather surprised. How much are you feeding? If the guppies are not getting enough, they may harass other fish.
The steps you are taking to solve the issue are very good so far; congratulations. If I had this situation, here's exactly what I would do:

1) Change 25% of the water every day, along with a gravel vacuum
2) Make sure the temperature is below 73F, to reduce stress
3) Continue your medication to treat the wounds
4) Remove any sharp objects that may be scratching the fish.

There is not much to do: you are on the right track.

In your 10 gallon tank, you may have some plastic plants. If you do, remove them, because they are notorious for injuring goldfish with their sharp edges. It may not be disease, but simply the harassment of the other fish, or the tank environment.

In the future, goldfish should be kept in an aquarium of no less than 20 gallons, because they produce lots of waste, and can grow to around 6"+ (for your species).

I hope your goldfish recovers!