@Rach please dont blame me if you loose anymore fish as I've given you the answers my friend all that come for free if you paid someone to look at your pond they would point out the same things to you.
Goldfish if propperly looked after can life as long as 40 years or more ith koi that figure goes up to 80 plus years or more so a koi will outlive a parrrot .
They are a living creature and as such we oe it to them to give them the best optimum conditions to live it , under the New Animal Welfare laws you are libal to prosicution in the UK if it is proven not enough care or attention has been taken Both the FBAS and the BKKS signed up to this after working out a framework with the RSPCA and other interested parties.
Our oldest koi is 28 years of age this year something we are greatly proud about because it shows care and attention to detail sadly we lost our other oldest fish "to old age aged 27", sadly it was a koi that didnt have the best strts in life and never really got over its close confinement with an oscar that badly mauled it when young (because someone didnt read up upon and didnt realize you shouldnt mix the two).
It never got above 6" and we were totally amazed it lived the time it did , the larger of the two 24" is still going strong but has been retired from the show ring and is now a pet.
So as you can see correctly looked after they can achieve great longeverly in life.
Dave