Distressing isnt it! more so when you cant see a reason, I trust you have ruled
out all the normal stuff like tested water for amonia, nitrite and nitrate etc? 
also check oxygen levels, a lot of people have plants in a koi pond and dont
realise they suck oxygen out of the water at night, to many plants results in
very low oxygen levels, and low oxygen will affect older larger fish first as
smaller ones need less oxygen.
 
If you have access to a microscope, do a scrape from a fish (live or dead)  and
a swab from the gills and test it for parasites, it is possible that you have
had a parasite explotion becasue of poor water conditions, it might look good
and crystal clear but it doesnt mean its at all healthy, so you maybe solve a
water problem but still have a major parastie problem, they have population
explostions in poor water conditions.

 I agree with edgar, the only change is the new filter, personaly i would never
buy a used filter of any kind, even if i knew where it came from, if the water
tests are fine them you should consider that your problem area.
 
I hope these pointers are of use.
 

--- On Wed, 8/7/09, Bob Cutrupi <bcutrupi@...> wrote:


From: Bob Cutrupi <bcutrupi@...>
Subject: [Worldwide Koi Club] Losing fish
To: worldwidekoiclub@yahoogroups.com
Date: Wednesday, 8 July, 2009, 5:07 PM








Hi, I'm a new member and I have a big prob;em with my koi pond. I live in NJ and
have had 2 Koi ponds for 10 years. Recently I have had a major problem with my
big pond. Its a 5000 gallon pond. The fish in the pond are 5-8 years old. Most
are 18-24 inches long and very healthy. A third of the fish are actually babies
that grew up. The pond has maintained 23 large fish for many years. I have had
no deaths until recently. In June 2009 I bought a used Bead Filter that was used
by a pond store indoors. I always had ultraviolet lights - but I decided to add
a new unit with 6 bulbs. I use a skimmer as well. I dont over feed them - once
or twice a day - as much as they can eat in 2-3 minutes.

The water never looked better.

In the last week I have lost 10 of my 23 Koi. I started treating my pond with
Melafix 2 days ago. Three fish died since the treatment started but I believe
they were already weakened.

I bought a testing kit and before I added any Melafix I got the following
results:

1) pH - 8.0
2) Amonia - 0
3) Nitrite - 0
4) Salt .50
5) Phosphate - . 50
6) KH - 135 ppm

I added a little more salt then started treating with Melafix. Today I added a
broad spectrum antibiotic that turned the water blue.

Do you think my fish could have caught something from the used bead filter?

My little pond is doing great and its next to the infected pond. I have made
sure not to use any nets or equipment that is used in the big pond.

I am going to have a necropsy done on the next fish that dies.

Any advice you can give me would be highly appreciated.

Thank you,

Bob Cutrupi



















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