indoor pond water quality

Question
I have an indoor pond with two koi and five catfish one channel and other four bluecat. The pond is about 700 gal. and the water has become milky looking. There is a white slime covering the liner. What is this "slime" and how do get rid of it. I have a 400gal. with same lighting and half the filtration filled with feeder fish (goldfish and guppies) not two feet from larger tank with no problems. If you need more info. just let me know. Thank You for any info. you can provide on this problem.

Answer
Hi,
It looks like a lack of oxygen in the water,doe's the filter need cleaning out? is the returning water from the filter splashing into the pond to aereate it?do you need an airstone in the pond?.
are your koi to large for the size of the pond ?
are their to many fish in the pond ?
I would check the above out and also do a gradual water change over a few days
George.