pH above nine would annihilate any aquatic life, so that's probably out of question... I think your pond is suffering from new tank (or "pond" in this case?) syndrome, and it may also be a bit crowded.
Here's what you should do:
- Test everything, and give exact results! pH, ammonia, nitrite and nitrate
- Buy a good water conditioner/bio filter booster. I've got Easy Life Fluid Filter Medium, which is pretty much a water conditioner and a bio filter booster in one so you won't need two bottles. Very good stuff! It will not only help the beneficial bacteria in the pond but also take care of smaller wounds and infections of the fish as well as strengthen their immune system. (It will also neutralize ammonia and chemicals)
- Do a major water change if anything's wrong, at least 50% and dose for the whole pond.
- See if you can get rid of the koi (as in: give away), because they will grow huge. They need lots of space, and might bully the goldfish.
- After this is done, add some anti-bacterial medication, no melafix, pimafix or any cr*p like that. It won't deal with any bacteria. But something for bacterial infections, something specifically for fin rot would be ideal!
- Now you should be testing the water daily, pH and everything else. Change a bit of water whenever the ammonia, nitrite or nitrates are too high. Always replace the dosage of medication, as well as the dose of water conditioner and bio filter booster.
- Observe your fish, and wait.