Ponds and koi and nitrites oh my

Szechuanosaurus

So we bought a house and it came complete with a pond with three koi in it.

I don't really know how to take care of fish or ponds at all or what normal and abnormal situations are. However...

The water has recently turned a cloudly greyish colour and the koi spend a lot of time with their heads above the water, sucking water in and spitting it out. At first I thought they were trying to feed but they seem to spit most of any food they happen to suck in.

So I've been reading snippets from a book about ponds and the colouring of the water and the behaviour of the fish may be a result of high ammonia or nitrite levels in the water (probably as a result of over feeding).

The pond doesn't have a filter fitted bit it has a self-circulating water fall. Unfortunately, attempts to turn this on have been unsuccessful, so I can't actively aerate the pond. I am going to be buying a garden hose soon, so I could set that to a fine spray onto the pond which can apparently help oxygenate the pond. I also don't have a pH meter or anything to test the water with.

What I'd like to know is, does this sound to anybody who knows like it probably is a problem with nitrite levels and if so, at this time of year, is a partial water replacement possible. If yes, does this just involve me emptying half the water out of the pond with a bucket and then refilling it with tap water or what? Is there any harm in doing this even if it isn't a nitrite issue?

Also any other comments, suggestions or advice.

Feral

I dunno about a koi pond but when I've kept freshwater fish in large tanks, surfacing behavior is indicative of having poor water quality (too much ammonia, too much nitrite, not enough filtering, not enough aeration) and a partial water change is usually what we'd do in that situation.

The only thing I'd keep in mind is to let any tap water sit and breath for a couple of hours before dumping it in the pond. I don't know if it's as important in a pond as it is in a tank, but when changing water out of a tank, the chlorine in tap water can shock and stress the fish. Chlorine evaporates off after a little while, hence letting the water breath for a bit. But I acknowledge that with an open air pond that might be unnecessary.

I can't think of any reason why you shouldn't do a partial water change.

blanknogo

They also sell this solution that removes the chlorine from the water. Even still though it would be a good idea to let the water sit outside for a few hours so that the temperature of the water you are adding in is close to the temperature of the water already in the pond.

In the future be careful of overfeeding. Food that doesn't get eaten rots and contaminates the water.