Hi
I've got a largish pond (20ftby 10ft) and max 2.5 ft deep. its got lots of marginals and plenty of oxygenating plants (elodea), also a large waterlily.
I've about 20 fish (goldfish, shubunkins ans a few golden orfe)which I've put in over the last three years, none larger than 5 inches.
in the last two weeks I've lost about 5 fish. they don't have any obvious signs of disease.
Any ideas?

Could you post the results from a set of water tests (pH, ammonia, nitrite and nitrate)? Also could you give some more info on the location of your pond, filtration and wether you have added anything to the pond recently (i.e. chemicals).

Thanks for your speedy reply.
The pond is in hyde, cheshire. Its about 4 years old and lined with rubber. I've added nothing to the water. no heavy rain recently so not much possibility of anything leaching into the pond. Haven't tested the water for nitrates, nitrites or ammonia. Someone suggested tonight that the deaths could be due to decaying plant matter producing these chemicals and it sounds like you are suggesting the same thing.I do have a u.v.and bacterial? filter and pump which I installed last year to combat an algal bloom. Not used it this year yet
I'll test the water as soon as i can get a test kit and let you know the results.

hi pleccy
just tested the water with tetra strips. Used 3 different strips to ensure a good result.
pH 6-8. nitrate approx 25mg/l, nitrite approx 1-5mg/l. not easy to be more accurate as the shadings on the test card are a bit difficult to discern. Certain though that the concentrations are no higher than I've mentioned. According to the pack these readings are a little high but not too high to necessitate change of water. What do you think?
Other tests on the strip were also ok. No facility to test for ammonia.
Yet another fish is on the way out- a 3'' goldfish. I netted it and there were no obvious signs of disease apart from 3 small patches approx 3mm across where the scales are silvery.
23rd march-another 2 fish down and one looking very sickly, just hanging about on the surface.I've cleaned and restarted the filter, removed 25% of the water and replaced it with tap water which has had the chlorine neutralised.