Quote:
Originally Posted by
zek 
Sorry you lost some of your fish.
How big is the pond and how long have you had koi in it? Is it a new filter?
How many fish are/were there?
If it's new test for ammonia and nitrites. It takes a few weeks for the filter to cycle. Clear "clean" water can be loaded with ammonia & nitrite. A little salt will help get you through the cycle if you have nitrites (1.5-2 lbs per 100 gallons). Use something like CloramX to lock ammonia until you cycle.
Of course it could be the AC mat too, but most of the mats are fairly benign. The larger problem is most of them will break down more readily in a pond environment. Their not made for filtering water, only air.
The people at koivet.com are pretty good at solving these kind of problems.
good luck and preserverence!