goldfish & Koi deseases

Question
The fish look like they have sores. It looks like the skin is being eaten away. Some look whit and other are red. I have a 2000 gal pond. I have a bialogical filter, skimmer and UV light. The golfish looked healthy swimming and eating until a day or so before they die. The marks seem to getting bigger and a few days. I have not lost my Koi yet. I have one with a mark on its back and it looks white(he is blue)
I have another one with a sore that is red. He is orange red & white. At the pond store they said it might be parasites and told me to put in Medifix medicine and pond salt. I took the gold fish out of the pond and medicated them but they still dies. My Koi are still in the pond. I have put lots of medicine in the pond. It has been 1 1/2 weeks since I treated the pond. I did it everyday for a week. I just noticed that more goldfish and Koi are getting the spots. So far they are swimming and eating good. I am keeping an eye on them and I am really concerned that I will lose all of my fish. I have also added fresh water. I appreciate andy suggestion that you can give me.
Marie
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Followup To

Question -
I am having a big problem with my fish. I have lost 5 goldfish so far and now I am noticing that some of my Koi have spots on them too. I have used medicine in my pond for ulcers and also pond salt. I am afraid that I am going to lose all my fish I had the water tested and they said it was okay. What should I do.

Answer -
What do the spots look like?  A good site to visit is koivet.com for koi health.  How big is the pond?  How big are the fish?  Are the spots white, black, gray, red, or what?  Are they raised or flat?  What other symptoms do the koi have?  You can contact me through my web site with answers to these questions so that I may be able to provide more information.  Good luck!

Robyn
fishpondinfo.com

Answer
It sounds like they could have Aeromonas which is pretty common with koi.  It's a bacterial infection.  I suggest buying some Koi Zyme (formerly lymnozyme). Here is the place that makes it:
http://www.koizyme.com/about.html

I ordered some for the first time this year from some company (forget which since I'd never ordered there before).

The marks could also be another sort of bacterial infection so antibiotics may help.  A natural one to try is MelaFix by Aquarium Pharmaceuticals.  I'm assuming you're in the US.  If not, you may not be able to get these two products.

In any case, the pond salt is a good idea, at 0.1% if you have no plants, no more than 0.05% if you have plants.

I hope this helps!