Hello and welcome. My name is ***** ***** I'm a biologist with a special interest in fish. I'm sorry for the loss of your koi.
This is a particularly difficult situation because we don't know how long the fish was dead. In cold water, a dead fish may be well-preserved, but it will become coated with slime. However, there are also several illnesses and parasites that can cause that jelly-like membrane.
Your instincts are good. You do want to do a water change of about 25%, and get the pump and bulbs operating. Examine all the other fish as closely as possible. If you see any signs of trouble, you'll want to treat with a good medication. If you don't see anything wrong, you'll have to make a decision. You can salt the pond and keep watching. The other option would be to go ahead and treat. If you choose to use medication, don't salt. TetraPond Treatment is a good medication that treats fungal and bacterial infections, and also parasites. It will not treat viral diseases because there are no medications that can do that. when a viral disease is present, we often lose many fish.
Here is a reputable source for the medication.:
This medication is a good one for situations like this, where we don't know what happened. If you have more questions, let me know. I hope all of your fish will remain healthy.
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