Expert: Brigitte - 7/7/2009

Question
Hello Brigitte
My Husband has a fairly new pond about 3 months,he was given some goldfish about 2 months ago(the owner said they were Koi but we didn't think so)they have been doing really well, we bought some others and still all well, then about a 10 days ago one of the fish we were given was dead, the next day 4 dead and then at least one daily since,our local aquatics tested the water he said it was perfect, we stopped feeding for about 3 days - made no difference, pump and filter working fine, plenty of oxygenating plants,we do notice that they go nearer the surface and seem slightly unbalanced when they swim and so far only the fish we first had, other than that we can see no sign of disease, I really hope you can shed some light on this question.

Answer
Hello Lesley!
It is always difficult to diagnose the problem from afar, but I would say this is some sort of water problem (no matter what the pet store says). What did they test for? How old was their test kit?
The first things to look at are: Nitrite, Ammonia and Nitrate. Any level beyond zero is deadly.
Next thing is oxygen level. If the fish are gasping at the surface they are not getting enough air for some reason.
This could be due to the above poisons, but also possibly because water is added to the pond without using de-chlorinator (chlorine damages their gills over time and they can no longer breathe adequately).
Best thing to do at this point:
a) stop feeding
b) do a couple of days worth of 1/3 water changes (be sure to de-chlorinate)
c) make sure that a fountain or waterfall is putting plenty of oxygen into the pond
d) buy a test kit (they are reasonably priced) that is fresh and test for the above values.