Question
QUESTION: hi i have a 150 gallon aquarium its a native uk setup it has chub carp bream tench and red fined perch.
i have a pond for the larger fish when they reach size.
all my perch are dying they have cloudy eye its passind from perch to perch i have treated them it clears up but they seem to keep catching it can you help.i have one healthy one left one sick one thats in a nires tank my waters fine and i do regualr water changes.

ANSWER: I need some more information.  What of your water chemistry did you test to be fine?

The cloudy eyes are just a generic symptom of declining health.

Are they clamping their fins?
Are they streaking/flashing?
Any tumors?
Red lines in the fin areas?
Lethargy?
Eating habits changing?
Gasping at the surface for air?
Hard, slime-less appearance or touch?
Anything else you can think of?

---------- FOLLOW-UP ----------

QUESTION: no other symtoms i use a api master test kit and check 5 diffrent things  

Answer
I don't know if you have a GH test in your kit.  High GH weakens the immune system over time and it can also account for the cloudy eyes.  Try testing general hardness.  It is also possible that your current tests have gone bad.  Not probable, but possible.