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what killed my fish?

Posted by Maria2013 5 (My Page) on
Fri, Apr 11, 14 at 8:49

I've had a koi pond for several years, (about 2000gl with 10 to 15 fish) I'm no expert but I've managed to keep my fish alive through the years, with minimum loss over the winter (lost only 1 last year, none the 5year before last)

This year as the snow started melting I started losing fish by one the largest (over 1') ones all died
I think I lost 7 or 8 , only 3 babies survived and I have no idea why it because we had a super cold winter and at times it was impossible to keep the ice open for aeration?
Is it because there was substances in the snow that got plowed onto the pond?
Do you guys have any idea why I lost all the larger fish and not the babies?
I would like to understand what went wrong so that it never happen again
Thank you

Follow-Up Postings:

RE: what killed my fish?

Hi Marie
This winter has been one of the worst in 20 years. How deep is your pond? Also, you say you started losing your fish as the snow started melting. Does this mean that you seen the fish alive under the ice or at the time of fish lose there was no ice on the pond?

RE: what killed my fish?

Hello Craig, and thank you for answering my post

The deepest section of the pond is a little over 3' deep

The first fish we saw, appeared at the opening of the ice, it was the largest fish in the pond, it wasn't dead, it was just floating near the opening (we keep the ice open with a few air stones) , at that time there was snow covering the rest of the pond, we couldn't really see any other fish, but it was clear that there was something wrong with that one the snow melted, we saw a couple more towards the top (they usually stay all together, at the bottom) but we could see the rest of them seemed ok as they occasionally passed by the clearing,
.... as the days went by, and snow melted , one or two a day detached from the group and started acting sick and eventually died ...I only have 3 fish left, all 3 were born last Spring.

so sad, I'm almost afraid to buy more fish :(

RE: what killed my fish?

I'm very sorry for your fish lose, you become really attached to them. If your like me you even name them. There are basically two occurrences that causes big fish lose, especially after a harsh winter.
The first is from poor aeration over the winter months and a build up of gases that are toxic to fish. Without a hole in the ice, these gases become trapped under the ice and result in mass fish lose. At first I thought this is what happened to your pond. However, I believe your pond suffered from the second occurrence.
Have you tested your PH levels? If so, test the pond early in the morning and later in the day. This winter has been especially harsh. Like most of our ponds in the northern region, your pond was covered with a blanket of snow most of the winter. It's not your fault, this was a really rough winter, and many people I know including myself lost fish.
As light begins to enter your pond, photosynthesis of your plants and algae on the bottom begin to work. This causes a raise in Ph. As the sun goes down, photosynthesis slows and this causes Ph to drop. Have you ever heard of a PH buffer or KH "Totally alkalinity". Now a good KH reading above 80 will prevent a massive swing of Ph.
This winter put a big strain on our fish with long periods of cold temperatures. This is my guess to what happened. If you don't know about KH and PH swings, this is what you can do.
First, check your water to make sure this is the problem. Start doing water changes, after water changes add 1 cup of baking soda for each 1000 gallon each second day. Tetra has a nice cheap Pond Test kit with dipsticks that read Ph, Total alkalinity, Total Hardness, Nitrites and Nitrates.
I hope this helps...


RE: what killed my fish?

Hi Craig,

Yes I too carefully pick my fish and give each one a name

This passed weekend we Spring cleaned the pond and filled it with fresh water, I will definitely get the PH buffer you mentioned in the hope that this doesn't happen again

Thank you so much for your advise, Craig, and sorry you lost fish too.


RE: what killed my fish?

Glad I could help Marie, I think I found that tester kit at PetSmart. Just remember that it is important to test your water during the winter months as well. Happy Ponding!!!


RE: what killed my fish?

I most definitely will test the water in the winter

thanks again for sharing your knowledge

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