[Isis]

Hi there,

I am having a problem with my pond, or rather the fish in my pond. My dear, dear fish. I have already lost two this week - both of them much smaller than the other fish in the pond - and more recent additions than the others. I have moved recently and the pond is only 5 months old. It's a liner pond, with no bottom drain (it is a temporary measure and am planning a proper pond). I had a single biological filter running with an 8watt UV bulb, which was insufficient, when I noticed the fish not looking to happy I put in another filter with a 15 watt UV light (this has only been going a week). I have two submersible pumps running the filters. I have 9 40cm koi in a 20 000l pond.

Fish behaviour - they are listless, they hang at the surface, sometimes head down, one of them breaks the surface quite regularly and seems to take a big dose of air. I inspected the gills of the dead fish and while their colour was not great, quite dark, aside from a little pond algae there doesn't seem to be any gill deterioration. One of the fish looks like it may have carp pox (small waxy swelling on mouth) and flukes toward the rear of the tail. I have a picture.

The most stressed fish have their back fins clamped (anal, ventral?) and are breathing fast. I have not fed since this started. Now for my water -

I did a 20% water change and used water conditioner half an hour ago and added a little salt and the water is as follows:

Ammonia - less than 1.2 but not 0
Nitrite - 0.3
Nitrate - 10
Ph - 7.5
General hardness - 60
Carbon hardness - 60

If anyone out there could please give me some advice on the best course of action before I lose more fish I would be eternally grateful.

Isis