why aer my fish dying

Question
I HAVE HAD FISH IN MY POND FOR 2YEARS WITH NO PROBLAMS I USE A BIOLOGICAL FILTER AND TREAT THE WATER. 3WEEKS AGO WE BOUGHT 7 KOI AND THEY HAVE ALL DIED WHAT ARE WE DOING WRONG?

Answer
How big is the pond?  What kind of filtration and aeration do you use?  Did you add dechlorinator or salt?  What do you use to "treat" the water?  It's a good idea to quarantine new fish.  Sometimes the fish may bring something into your pond and kill your old fish too.  Other times, the new fish simply can't adapt to your water for some reason, usually it's too different from what they are used to.  Did you test the water's pH, hardness, chlorine, oxygen, ammonia, nitrite, and nitrate levels?  If not, it's a good idea to rule those out.  Did the new koi have any symptoms before they died?  How big were the new koi? What other fish do you have?  I hope your remaining fish are okay!

Robyn
fishpondinfo.com