What's Up With My Fish?

[Mehitabel]

Sorry if this is a much-asked question or the answer's obvious, but I'm a newbie and the symptoms are confusing me.

I have a 750L pre-formed pond. About half of it is full of elodea canadensis. There are several marginals too. I have a Hozelock "EasyClear 3000" combined filter/fountain, which I run all year. But for the last 10 months, its UV light has failed to work, so the pond has gone very green and murky.

There are four small goldfish in the pond. They've done well for five years. But I've noticed that the smallest has developed what looks like algae over most of its body. To the naked eye, it looks green. But when I took the photos, it showed up as white in places..(Ich?) I also see from the photos that the scales look roughened. Can anyone help, please? What is this?

This particular fish also has a strange kink at the base of its tail, which dates back before the scale problem. It hasn't seemed to be a cause of stress, but I'd be interested to know what it might be.

I've done a water test :

NO3 = 0
NO2 = 0
pH = 7.5
KH = 80
GH = 120

I'm in the southern UK.

Thanks.

 

[MitchM]

Hi Mehitabel,
Two questions to start:
Has that fish been your pond for 5 years?
What are you using for water tests?

 

[HomerJay]

Are you able to test for ammonia? Do you ever do any water changes? That fish almost looks stunted in growth. Have you had it since it was smaller? Are it's scales usually flat? It could be age taking over, it's hard to tell from the pics.